"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"
The Deck relies on "Venom Swamp" for Venom Counters to have any effect on monsters, so if "Venom Swamp" is destroyed, Venom Counters are almost useless. This bad situation can be avoided by "Spell Reclamation".
The main weakness of the "Venom" Deck 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. 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 makes the ATK of "Vennominaga" become 0, and when it is destroyed by battle there are no Reptile monsters in the Graveyard to banish in order to Special Summon it again. To stop this, "Field Barrier" can be used to prevent the opponent from playing a Field Spell Card, while also protecting your "Venom Swamp".