Allergic Temmie was added in Beta 9.0 alongside Temmie Statue. Previous Versions can be found here.
Card Skin (Allergic Temmie)

Sick Temmie

Allergic Temmie has the ability to deal 1 damage to all enemy monsters whenever a Tem is summoned, making it act like Woshua. This even happens when an enemy Tem is summoned while you have one on the board.

This means that if you have an Allergic Temmie on the board, the enemy can't place a Temmie or Temmie 2 of their own, because they only have 1 HP, making them die instantly. (It can be canceled out with the help of Diamond Boy 1, though.)

Card Skin: Sick Temmie