Thelonious Viper with "Venom Boa", "Venom Serpent" and "Venom Snake".
"Venom" (ヴェノム Venomu) is an archetype of cards used by Thelonious Viper in the Yu-Gi-Oh! GX anime and introduced in Tactical Evolution. They focus on the distribution of Venom Counters via "Venom Swamp", while their strongest monsters (which are not technically a part of the archetype, but related to it) gain ATK for each Reptile-Type monster in the Graveyard. "Vennominaga the Deity of Poisonous Snakes" gives an alternate win condition via its Hyper Venom Counters.
Since they rely upon Reptiles being sent to the Graveyard, Venom Decks are at their most vulnerable when banish strategies are used, like "Dimensional Fissure". They are also at risk of losing Life Points early, since the only reliable methods for quickly Summoning "Vennominon the King of Poisonous Snakes" from the Deck involve taking Life Point damage (either via "Damage = Reptile" or "Damage Condenser".) All other "Venom" monsters happen to have low ATK for their Level as well, so it is difficult for a "Venom" user to take the offense to the opponent early, especially if "Venom Swamp" is not yet on the field.
The Deck focuses on lowering the opponent's monsters' ATK with "Venom Swamp" and Summoning "Vennominon the King of Poisonous Snakes" or "Vennominaga the Deity of Poisonous Snakes". Since the ATK of both cards are dependent on the number of Reptiles in your Graveyard, cards like "Foolish Burial" and "Snake Rain" are important in this Deck. Also, there are not many "Venom" monsters, so a hybrid with other Decks is inevitable.
"Venom Swamp" is able to quickly weaken and eventually destroy any non-"Venom" monster. Also, even if "Venom Swamp" is not on the field, "Venom Burn" can inflict serious damage to a player's Life Points. In addition, the ace card of this Deck, "Vennominaga the Deity of Poisonous Snakes", is almost invincible since it cannot be destroyed by any means except by battle, and can only leave the field by Tributing it with cards like "Volcanic Queen" and "Lava Golem", though even this can be countered with "Fog King" or "Mask of Restrict".
The Deck relies on "Venom Swamp" for Venom Counters to have any effect on monsters, so if "Venom Swamp" is destroyed, Venom monsters' effects are useless. This bad situation can be avoided by "Spell Reclamation". This will greatly help in a Venom Deck, as when Venom Swamp is destroyed, it is returned to your hand. In addition, Summoning "Vennominaga the Deity of Poisonous Snakes" is difficult since you need to Summon it with "Rise of the Snake Deity", meaning that a mere "Seven Tools of the Bandit" or even "Malfunction" can ruin your chance.
The main weakness of the "Venom" Deck, however, is the low ATK points of most "Venom" monsters. This means that your opponent can easily just Summon a monster to destroy your Venom monster, ignoring "Venom Cobra". Because of this, cards like "Ambush Fangs" and "Negate Attack" are essential to this Deck.
Another weakness of this Deck is "Zombie World". This card should make the ATK of "Vennominaga" 0, plus when destroyed there would be no Reptile monsters to banish for bringing her back. To stop this its important to have a "Field Barrier" protecting your "Venom Swamp".
- "Evil Dragon Ananta" – In the event that attempting to Summon "Vennominon" or "Vennominaga" fails, this card can be used as a backup by banishing all Reptiles on your field and in your Graveyard.
- The Tyrant Neptune – If you find yourself without "Venominon", this card works as a backup plan. Tribute Summon this card with at least 1 Venom Effect Monster to make this card immune to the effects of Venom Swamp and allow it to distribute Venom Counters in place of your weaker monsters. Also, if "Vennominaga" is destroyed and there are no Reptiles left to banish, use this card's effect to gain "Vennominaga's" ability to gain counters for an instant win.
- "Snake Rain" – Sends 4 Reptiles to the Graveyard from the Deck, powering up Vennominion or Vennominaga by 2000 ATK. In addition, if you discard a Reptile monster for the cost, that's another 500 bonus ATK points.
- "Damage = Reptile" – Allows the easy summon of "Vennominon", since his original ATK is 0. However, make sure to have at least a few Reptiles in the Graveyard before Summoning him with this.
- "Snake Whistle" – Summons another low-level Reptile when one you control is destroyed by effects, which can be handy.
- "Damage Condenser" – Allows the Summon of "Vennominon" in the event you do not have any Reptiles on the field at all.
- Destructive cards that target your own monsters – Since "Rise of the Snake Deity" cannot activate in response to cards that would make "Vennominon" leave the field without destroying it, it is usually more reliable to destroy "Vennominion" yourself. The Trap Card "Offering to the Snake Deity" was specifically designed for this effect. "Tribute to the Doomed", "Offerings to the Doomed" and "Hammer Shot" are some of the other better choices for this. Note that cards like "Thunder Crash" won't work, since they cause "Rise of the Snake Deity" to miss its timing.
- Non-Venom Reptiles – "Vennominon" and "Vennominaga" benefit from any Reptile in the Graveyard, not just Venom monsters. Some of the better ones to include in a Venom Deck are Reptilianne and Worm monsters.
- "Vengeful Bog Spirit" – Prevents monsters from attacking on the turn they are Summoned. When "Venom Swamp" is in play, this will weaken opposing monsters by 1000 ATK before they are able to make their first move. If you have a face-up "Venom Boa", this will mean that most non-Tribute monsters your opponent Summons will be destroyed before they even get a chance to attack with them.
- "Stumbling" – Like "Vengeful Bog Spirit", this makes monsters lose 1000 before attacking, and combined with "Light of Intervention", means that your opponent can only Summon monsters in face-up Defense Position; however, this also applies to you, so can also cause the same issues for your non-Venom monsters. This can cause problems without "Venom Swamp" or if they have a monster which can survive long enough with enough attack to destroy your defense position Venom monsters, however unlikely that is.
- "Light of Intervention" – "Venom Swamp" can't place counters on face-down monsters, so this card prevents your opponent from Setting their monsters.
- "Final Attack Orders" – Allows "Vennominon" and "Vennominaga" to inflict battle damage very easily, especially since Vennominaga cannot be equipped with a card that would grant it piercing damage. Activate "Final Attack Orders" only when ready, however, as most Venom monsters are quite weak.
- "Solidarity" – Boosts the ATK of your "Venom" monsters, which alleviates their main survivability issue. If you use this card, you cannot use non-Reptile-type monsters, although not many would fit into this Deck anyway.
- "Viper's Rebirth" – If you're using "Solidarity", use this card as well. The best use of this card is to Summon "Vennominon" and let it destroy itself, thus triggering "Rise of the Snake Deity". Also, since the effect takes place during the End Phase, Summoning "Vennominaga" is faster.
- "Venom Burn" – Helpful if you're racing your opponent for damage and you need that last little push for the win. A particularly useful strategy is targeting your own monsters. If you're running non-Venom beatsticks like "Evil Dragon Ananta" or "Earthbound Immortal Ccarayhua", it instantly brings them back to full strength and hits your opponent hard for damage in a devastating one-two blow.
- "Metal Reflect Slime" – A very useful stall card. Not only is its 3000 DEF capable of blocking attacks from most monsters (a trait that is powered up by Venom Swamp's ATK-reducing ability), but its 0 ATK makes it immune to "Venom Swamp". This will keep it on the field both for defending against your opponent and accumulating Venom counters that you can use as ammo for "Venom Burn".
- "Alien Brain" – Allows you to use your opponents monsters to build a defense and stall for time. The newly acquired monster will also be treated as a Reptile-Type, so it gains synergy with your other Reptile support.
However, adding non-Venom Reptile-Type monsters can be a disadvantage, because while "Venom Swamp" is on the field all non-Venom monsters will be affected and potentially destroyed. However, you can use "Venom Burn" to remove Venom Counters from your monsters and inflict damage to your opponent.