Engage the Enemy

Engage the Enemy is Disc 1, Track 9 on the Xenoblade Original Soundtrack. It plays during cutscenes before and after important boss fights in the game:

Xenoblade Chronicles

 * Metal Face attacking Fiora in Colony 9
 * Before the battle against Xord in the Ether Mine
 * The cutscene between the two phases of the Leone Telethia
 * Metal Face appearing on Prison Island
 * After the fight with Mumkhar on Valak Mountain
 * After the battle with Mumkhar in Sword Valley
 * The battle between Zanza and Meyneth in the Mechonis Core
 * Between the two phases of the battle against Dickson

Future Connected

 * When the Telethia destabilise the Fog King's rift, allowing Melia to finish it off.

In Super Smash Bros.
A shortened and looped version of Engage the Enemy is one of the music tracks in both and, available on the  and (in Super Smash Bros. Ultimate) the  stages.

Trivia
There exists a post-battle dialogue in Xenoblade Chronicles 2 between Ursula and Rex during which they sing a tune that sound very similar to Engage the Enemy. There is also a similar dialogue with Electra.