I'm not sure how powerups will work yet; if they will be collected in-game or purchased between games, but I should hopefully be able to adapt the ideas to fit whatever system I eventually decide on.
So without further ado, here is the list:
Defense - 5
Mirror Attack - All projectile/melee attacks are reflected back toward the offending player. Melee attacks cause instant damage on the aggressor, ranged attacks are literally reflected back.
Holo field - Causes 2 ghostly occasionally flickering versions of your Orb to appear and follow you around in order to confuse an attacker.
Phase Shift - This powerup allows you to avoid all attacks for a set period of time, but you cannot use other powerups whilst this one is active.
Bumper - This powerup turns your orb into a bumper... any players orb that comes into contact with you will be sent bouncing in the opposite direction at high speed.
EMP - Disables all active powerups of all players
Offence - 5
Ram - Orb splits into two halves, front half shoots forwards and can be used as a method of ramming the opponent.
Self Destruct - Orb flashes 3 times during a 3 second countdown. Orb explodes at end of countdown dealing major damage within a large radius. Can be aborted part way through if desired.
Blast Mine - Orb can drop a limited number of mines which have a 3 second proximity delay and cause knockback/damage.
Spikes - Give the player more grip and cause damage on contact with opponent.
Gyro-mounted Lasers - Allow the player a limited number of laser shots to damage opponent. No knockback.
Movement - 5
Teleport (or Quantum Improbability Drive :)) - Allows the player to teleport to a position indicated by the mouse cursor.
Jet Pack - Allows the player to cross gaps in the arena and perform a drop down smash attack.
Inertial dampeners - Allows the player to instantly bring the Orb to a state of rest, regardless of current momentum.
Speed Boost - Boosts the speed of the Orb.
Grappling laser - Allows the user to cling onto objects to avoid falling, also allows players to cross difficult parts of the arena more easily. Can grab onto opponents to get them to effectively tow you along!
Physically Altering - 5
Body Swap - You and a random opponent immediately switch physical locations.
Grow - You become larger.
Shrink - You become smaller.
Invisibility - You disappear from view for 10 seconds, or until your first collision with another player.
Electromagnet - Nanobots within a set radius are attracted to you automatically.