Main Deck: 41
3 Ash Blossom & Jouyous Spring
3 Ghost Ogre & Snow Rabbit
1 Maxx "C"
2 Zoodiac Ramram
2 Zoodiac Ratpier
3 Zoodiac Thoroughblade
3 Zoodiac Whiptail
1 Dark Hole
2 Enemy Controller
3 Fire Formation - Tenki
3 My Body as a Shield
3 Pot of Desires
1 Soul Charge
3 Twin Twister
3 Zoodiac Barrage
3 Dimensional Barrier
1 Zoodiac Combo
This post will explain a lot of basic stuff that may already be obvious to experienced users, but will be helpful for those who are still learning. I think it shows how I go about deck building as well.
This list assumes your opponent is likely on Pure Zoodiac, possibly on True Draco Zoo, a very low chance of True Draco / Paleozoic / any rogue deck. I think that's the current warring meta. IRL, you may be somewhat more likely to face True Draco Zoo over Pure Zoodiac, and you will definitely face more rogue / budget / weird decks, but I think this list is perfectly viable to play at tournaments as well. You may want to make a few adjustments depending on your meta-call, but in general your deck can beat all worse decks anyway, so you will main and side to deal with the Zoodiac and the True Draco cards, since those 2 engines are the only real "threats".
There's no real reason why I'm at 41 cards atm other than: I recently made a few changes and don't know what to cut yet. If I were to move something to the side deck, I'd cut the 3rd Magic Deflector from the side.
The way I view this deck, if you have any Zoodiac card, you can "keep going" from there. So going first you want to open a Zoodiac and play around hand traps. Then, you want to establish the board that's the hardest to break for your opponent. So you want your board to be as big as possible, and you want to have as many layers of defense as possible as well. Traps are good going first, Spells are good going second, but in general you want to main cards that are good both going first and going second, and side into cards that are specifically good going first or going second.
Zoodiacs: Deciding the amount of normal summons and deciding which Zoodiacs are more important to play than others.
With 13 normal summons, you have an over 90% chance of opening a normal summon, and over 95% if you include Barrage. Barrage counts in the sense that, if you open it, you can make plays, but it doesn't count in the sense that it's not a normal summon. Something I think a lot of people fail to understand is that you don't want to optimize your build open a play to "not brick", but rather, you want to optimize your build to open multiple layer of plays. What this means is you want to open a normal summon AND Barrage, because it'll make your field better, and it'll play through Ogre / Ash, and it'll play through non-barrier traps or Drident going second. This is less relevant now, but for example in Norden format, it was very relevant (where you'd want to open Terrortop + Barrage + normal summon, instead of just opening 1 of these without the others).
Another thing that I think is important as to deciding how many of each Zoodiacs you run, is looking at what they do in your opening hand. Zoodiac Ratpier can play through Ogre, so that's preferable over another Zoodiac. Zoodiac Thoroughblade can help to turn monsterclogg hands into decent hands, so adding additional copies of Thoroughblade doesn't really count as adding more normal summons, as compared to adding Whiptail and Ramram that don't have this ability. Fire Formation - Tenki isn't an in-deck resource, has negative synergy with Pot of Desires, the 100 ATK gain can be relevant, but most importantly it can be Ratpier (to play around Ogre) or Thoroughblade (to turn brick hands into live hands). There's also the amount of Zoodiacs that you need to play "at least", in order for your deck to work. And there's also the fact you don't want the monster count to conflict with Pot of Desires. This all doesn't seem too relevant since the main build seems to almost maximize on all Zoodiacs anyway, but it matters while siding. I preferably wouldn't go below 2 of any Zoodiac because of Desires, and I wouldn't cut Thoroughblades/Tenki's. (So for example, if I wanted 12 normal summons, I'd go: 2 Ramram, 2 Ratpier, 3 Thoroughblade, 2 Whiptail, 3 Tenki. If I wanted 11 normals, I'd go 1 Ramram and just accept it when I banish it with Desires. If I wanted 10 normals, I'd have to consider if the 2nd Whiptail is needed, which it probably is, so I would have to cut Thoroughblade or Tenki: I'd cut Thoroughblade first, as Tenki can potentially play around Ogre. I don't think going lower / cutting Tenki's or Thoroughblades would ever be needed as to not clogg, since they already prevent clogging ). Losing to Ogre with Thoroughblade if you don't open an out to it is an concession I'm willing to make if the alternative is that I'm opening a monster clogged hand and am probably losing the duel anyway.
I side out 2 normal summons going second, because you open with 6 cards in hand instead of 5, and odds of opening one normal summon are still 90%+. There's also the fact that you "need" those other cards to stand a chance going second, so you may even want to side out 3 normal summons as well, simply because an ideal opening hand is something like: hand trap + out to drident + layer of play (barrage, twin twister, soul charge) + zoodiac, and you can't open that if you open 3/4 zoodiacs all the time.
Pot of Desires
I think this card is a staple at 3 because the odds of drawing 2 are still very low, the odds of banishing a significant amount of Zoodiacs is very low, and the only thing that's bad to banish is Zoodiac Combo, but odds are you open Ratpier or Tenki to begin with. Hands can get awkward sometimes where you don't know in which order you should active your cards, but in general you want to resolve as many search cards as possible. So for example if my hand includes Soul Charge, Zoodiac Barrage, My Body as a Shield or Pianissimo, I will resolve Ratpier, Broadbull, etc. before I will active Pot of Desires. I think this card is crucial cause it does everything you want a card to do: it increases the odds of opening a Zoodiac monster (not bricking), without decreasing the odds of opening layers of defense / ways to disrupt your opponent's field (which happens if you add additional Zoodiacs to your deck). Going second it's especially important because going second is just tough. It's literally Pot of Greed, it does so many good things, that I can't ever see myself not running 3 copies. I even run 3 in True Draco Zoodiac. This card solves all issues the deck has.
Maxx "C" is a staple and you side it out vs True Draco. Ghost Ogre and Ash Blossom aren't staples imo, even though I think they should be played and a lot of people are starting to main them as well. These cards are really tricky because they're sometimes good and sometimes not, and good vs some decks and less good vs others. But I decided to main them for a couple of reasons. They make the True Draco Zoo match-up outright favorable since the card really shines there. (It hit the same things it hits vs pure Zoodiac, with the addition of Terraforming and Diagram, which are both very good hits since the deck is a combo deck, odds are they'll brick after you block Diagram, or at least their play will become less explosive. If you don't block this, they can also extend their plays with Ramram to make matters worse). But that's not the reason I main it, since I expect most people to be on Pure Zoodiac anyway (and True Draco Zoo can be taken care of with the side as well). I initially thought these cards were bad vs pure Zoodiac. They never seemed to really do anything. Yes they block Barrage but using Ash on a Tenki or Broadbull is extremely subpar, they can play around Ogre with Ratpier anyway, and it's only really good vs Zoodiac Barrage. At least that's what I thought at first. I've come to appreciate these cards more because I view the mirror match differently now. Going second, you don't need to "just" open a Zoodiac + a way to out Drident + a way to play around/through their traps and hand traps, you also need to prevent them from making a big field. If they open with 4 Zoodiac monsters, resolve Thoroughblade/Combo for draw X, you're not going to win that duel to begin with. There's another reason why Ash specifically has gotten better: people maining Pot of Desires. Here's how I play these hand traps now, against pure Zoodiac. I will Ghost Ogre a monster because if they have MBaaS I want to make the trade to get rid of it anyway. Holding it for Zoodiac Barrage doesn't seem worth the risk because either way you're blocking a layer, so if I block their normal summon, and they have to make a board with Barrage now, their board will have taken a "hit" regardless. These cards are also just extremely versatile: good in different match-ups, good going first and second, they hit their nuts openings (Barrage, Desires), and they're good early and late game. This is what makes these cards better than stuff like Droll Lock, Ghost Reaper, those cards are very bad topdecks and bad going first. Combo is also a good target to Ash. If I see people use Terraforming, Diagram, Desires, Demise, Barrage, I'll Ash/Ogre it ASAP. Of course this depends on the situation, but in general I think that's correct. I don't want Ash on Tenki, Broadbull, Thoroughblade, unless if I know they don't have monsters or they need to topdeck an out. The additional benefit of maining hand traps is that you can effectively side into Flying "C" going second. When you do, you Flying upon summon, and use Ash/Ogre on Barrage so they can't out it. Yes they can Missus it away, but you've still essentially killed their play for the turn. The only real "out" then, outside of them opening Barrage and you not opening Ogre/Ash, is Soul Charge after they've summoned Missus. Flying is a worse topdeck, but not completely dead, it does have some mid/late game playing value.
Raigeki, Dark Hole, Enemy Controller, My Body as a Shield, Book of Moon, Pianissimo, and the lack of Forbidden Chalice, Kaiju, Shuffle Reborn
All these cards can out a Drident going second, so you need to open at least one, but they aren't equally good. You don't want cards that lose to Hammerkong, so you don't want outs that target. Kaiju is a reliable out, but if they have a trap to stop your Zoodiac play, it can come to bite you back in the ass later on as they're beating you down with it. It can also be difficult to deal with, since you have to either run over it or waste a Drident effect on it, and if they have a big field that's not always possible. A better alternative, then, is Santa Claws, which you can attack and banish with Whiptail, but that has issues as well because now if your Zoodiac play gets stopped, they get the draw. They also suck going first. I think Shuffle Reborn is good going second but bad going first, outside of playing through Ghost Ogre, since it isn't a layer of defense, even though it's not completely bad. I don't know why I haven't included it, I guess other cards just felt more urgent. I would side it for going second since it can play through True Draco traps as well, it may be better than Pianissimo going second. Book of Moon is really good to lock their EMZ out, but I moved it to the side cause it loses to Hammerkong going second. My Body as a Shield is absolutely fantastic. Going first, it plays through Ghost Ogre, and protects your board against Dark Hole, Raigeki and Drident. This allows you to end on Hammerkong instead of Ramram as well. Going second it plays through Drident, Torrential Tribute, and opposing MbaaS's (if used on your Drident only), as well as Ghost Ogre. Doesn't lose to Hammerkong. Enemy Controller was originally in the side deck but it's just pretty going. Going second you can summon a monster, and if it gets Dridented, you tribute it to take their Drident. If they have Hammerkong, you do the same but take Kong instead, overlay your own Zoodiacs, and either destroy their Drident by battle or by your own Drident's card effect. Also clears Flying "C", even if people are cutting that now, I still think it's relevant because that card just steals games. I think the only real exceptions to my own rules are maining Raigeki and Dark Hole, which aren't a layer of defense going first. I originally didn't play them to play around MBaaS and Ramram fields, but I realized that's dumb. You have to eat the MBaaS at some point anyway, so it's a good trade to make, and a field of 3/4 monsters including Ramram is a lot harder to clear than simply just a Drident with a Whiptail attached. Based on this, I had put Raigeki and 2 Dark Hole in the side for going second, but it's just so good and necessary to win going second that I decided to main it. I may end up putting 1 of these 4 cards into the side again if I think going first becomes too weak, but the reason I'm not maining 3 E-Con 3 Shuffle Reborn 2 Dark Hole 1 Raigeki, is because I don't want to make going first too weak, even if these cards aren't completely dead, I'd still rather have something else. Enemy Controller is actually pretty good going first sometimes. If you open 3/4 monsters you can take their monster which is just as good as a trap. If you open 2 monsters (likely Drident + Hammerkong, Drident + Missus Radiant, or Drident + Ramram), it becomes worse, but with 2 Ratpier 3 Tenki 3 Barrage 3 Desires, odds are you'll open a better field. So essentially what I'm saying is E-Con is good going second, kind of good going first when you open Ratpier Tenki or Barrage, which makes it mainable, but you could still either keep it in or side it out going first. The 3rd E-Con is sided, which you bring in going second, obviously. You also bring in the 3rd Dark Hole going 2nd, and side out Raigeki Dark Hole going first.
Twin Twister, Cosmic Cyclone
Cosmic Cyclone is amazing vs True Draco Zoo going first (hits Diagram, Heritage, Disciples) as well as going second (you can chain it to their Return or Apocalypse). Against pure Zoodiac though, I just think the card sucks. It's a worse Ghost Ogre going first, since it's only good vs Zoodiac Barrage, and going second you're going to hit a backrow and hope you miss Dimensional Barrier. Twin Twister may be more inconsistent: it's worse vs True Draco Zoo going first (good going second), it's potentially worse going first vs Pure Zoodiac (worse to hit Barrage, but if it's G1 and they set a bunch of traps, it's still fine to hit those in the EP), but going 2nd vs Pure Zoodiac is where this card shines. If they set 2+ backrows, you want to hit as many as possible to even give yourself a chance of winning the duel. For this reason, I main 3 Twin Twister. I side them out going first. I side in Cosmic Cyclone against True Draco Zoo both going first and second. Going first against Pure Zoodiac, I play neither.
This is the kind of card that's better going first than going second, but I main it because it's just auto-win going first and still pretty decent going second. It's the kind of card you want to have as your 3/4th card in your hand. For example, say you want to ideally open: Zoodiac, Barrage, Dark Hole, Twin Twister, or something among those lines, then Dimensional Barrier is just there to ensure you win the grindgame once you've killed their field. It's just good, and the only trap I'd consider maining (don't really count Combo as a trap).
Imperial Order is sided going first against anything, Magic Deflector is sided going first against True Draco Zoodiac and it's pretty good since it plays around Cosmic Cyclone/Twin Twister in case they're on that as well. Pianissimo is pretty good going first (essentially another MBaaS: lets you play through Ogre, Dark Hole, Raigeki, and making monsters undestroyable by battle is pretty solid as well). I may want to side Shuffle Reborns going second, idk, I don't consider the card bad.
I think if you open Ratpier or Ratpier + Barrage, you shouldn't go for Missus + Drident or Emeral + Drident plays. Instead, go for Drident + Kong + as many Zoodiacs as possible (while spamming Thoroughblade draws, ended on Ramram, etc.) Missus is good but you want to save it for next turn, to OTK. Kong is better cause it makes Drident harder to get over. Having 3-4 Zoodiacs is better than having 2 monsters, because even if your opponent can get past Drident, it's still harder for them to clear all. This is also the reason I don't play rank 4's in my extra, it's not that the Zoodiac xyz's are absolutely necessary, it's that I don't think the rank 4's are ever really worth it to make (and they require you to open the nuts to begin with). Yes Dweller going first vs Draco Zoo is cute, but that's extremely niche since you don't know what deck they're on to begin with, and G2/3 you already side in Magic Deflector/Cyclone etc. Kong is also strong vs them.
Playing around Ash
You want to bait Ash by playing Tenki, Broadbull, before you play Pot of Desires.
Playing around Ogre
When you can play around Ogre, you want to. So if you open MBaas, Soul Charge, Zoodiac Barrage or Pianissimo, you can "go nuts" with your Zoodiac plays, but if you don't, and you open Tenki or Ratpier, you won't use the effect of Ratpier. If you open none of these cards at all, you just have to play into it and hope they don't have it, cause if they do you'd lose anyway. My priority with Ratpier is to get Combo to the grave, after that to try to get Ramram out of the deck (in case of Desires), Whiptail in hand, Thoroughblade in grave, etc.
Playing around Dark Hole, Raigeki
By keeping a Ramram on the field and a Whiptail in hand, you can special summon Drident from your graveyard the moment they Dark Hole or Raigeki, attach Whiptail to it, and you have effectively "saved" your field.
I haven't covered everything, but I think I've covered a lot. I was going to mention more things with regards to technical play etc. but I kind of forgot since I've been playing Goat Format all day. I guess just ask me what you want to know. If I think about more I want to share, I'll edit it in. I'll plan on making a similar thread for my True Draco Zoodiac, which will contain some surprising choices. I don't think there's a clear "best deck" between Pure Zoodiac or True Draco Zoodiac, I think both decks are viable and "it depends".