Characters with Biotics:
Most Biotic powers will cause an enemy character to be knocked off their feet. Some even pull them through the air or push them distances to the ground.
Starting the combo with a pull is usually the easiest, then hit them with any other biotic power.
If you are a Biotic, to use your power hold RB and highlight the power you want. 1 allie MUST also have a Biotic power, highlight that next. OR use the power mapped to one of your hot buttons for both you and your allie.
If you are not a Biotic, 2 allies must have Biotic powers, hold RB and highlight one power (pull is best) then highlight another power with the second allie. OR use the powers mapped to the allies hot buttons on the D pad.
Note 1:D pad (right and left) only will send a pre set power at an enemy if they are highlighten on your screen. Otherwise it orders the allie to a location
Note 2: favorite combo is a pull followed by Miranda's 'Slam' move.