Bahamut SIN (バハムート震, Bahamūto Shin?, lit. Bahamut Tremor) is a form of Bahamut summoned by Kadaj's Summon Materia to destroy the Meteorfall monument in Edge, as well as wreak havoc on the populace, in Final Fantasy VII: Advent Children.
The party members of Final Fantasy VII engage it in battle and it is ultimately destroyed by Cloud's Climhazzard Limit Break.
The attack Bahamut SIN uses in the game is not named in Advent Childre nor related materials. However in Final Fantasy VII, each form of Bahamut uses an ability whose increases in SI prefix starting with Bahamut and Megaflare. The third, Bahamut ZERO, uses Teraflare, and Bahamut Sin's successor, Bahamut Fury, uses Exaflare. Therefore it could be assumed Bahamut SIN's ability is Petaflare. Bahamut SIN's strongest ability in Final Fantasy Record Keeper is Petaflare.