Co-Op Event 7: Battle of the Dark Sides
From SmashWiki, the Super Smash Bros. wiki
Battle of the Dark Sides (死闘、ダーク軍団, Fight to the Death, Dark Corps) is the 7th co-op event match out of a total of 21 in Super Smash Bros. Brawl. Player 1 controls Link, while Player 2 controls Samus. This is similar to the solo event Event 18: Dark Link Duel, but Samus has been added to both teams. Each player has 200 HP, and the event is completed by dropping both the CPUs' HP to 0.