New boss: Dark Samus.
Has to stay charged to stay moving and attacking.
Tools:
Recharge tool - Refills the energy bar after a quick pause.
Phazon Scattershot - Fires many small projectiles in a hose-like fashion. Drains energy quickly, can be sustained for a few seconds.
Shield-wave: Creates a quick shield around the player, knocking away both players and projectiles. Can be used a few times before needing recharge.
Missile Launcher: Fires missiles, similar to Samus. Can be charged for a super missile. The missile fire rate is noticably faster than that of Samus. Missiles can be fired up to 4 times before requiring a recharge, though it is never advised to completely drain your energy, because you cannot move or jump at 0 percent. Super missiles drain 80% of energy, but will only fire a normal missile if you have less than 50%.
To put it simply, just fight like normal but don't let your energy run out.