Nidoking 11/102 - Base Set Holofoil

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

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).