Annihilator X means that whenever a creature attacks, the defending player sacrifices that number of permanents.The defending player chooses what to sacrifice, often lands or tokens.
Sneak Attack, Through the Breach, and Eldrazi Temple let annihilator creatures come out and attack far sooner than their mana costs suggest, while It That Betrays steals the nontoken permanents opponents sacrifice. Eldrazi Conscription grants annihilator 2 to any creature, and extra combat effects multiply the triggers. Annihilator only affects the player being attacked, so in multiplayer games it's best aimed at the opponent with the strongest board.
