Koga's Weezing.

Flip a coin. If heads, this attack does 10 damage plus 30 more damage and Koga's Weezing does 30 damage to itself; if tails, this attack does 10 damage.

Flip a coin. If heads, the Defending Pokémon is now Poisoned. It now takes 20 Poison damage instead of 10 after each player's turn (even if it was already Poisoned).