Here is the full list of all 21 Alien Breed trophies - there are 21 bronze.
SCORE 17,171,717 POINTS TOTAL SINGLE OR CO-OP PLAY
PURCHASE ALL WEAPONS FROM THE SHOP
SCORE 1,000,000 CO-OP POINTS ON A LEVEL
KILL 50 ALIENS DURING A COUNTDOWN
COMPLETE ALIEN BREED
DEFEAT A BOSS ALIEN TOGETHER WITH FLAMETHROWERS
COMPLETE ALIEN BREED SE LEVEL 11 IN CO-OP WITHOUT TRIPPING THE ALARM
DIE TOGETHER IN THE MASHERS ON CONVERGENCE LEVEL 4
COMPLETE 17 CO-OP GAMES
COMPLETE A LEVEL IN CO-OP
KILL 2 ALIENS WITH ONE SHOT
DEFEAT A BOSS WITHOUT FIRING THE ASSAULT RIFLE
COLLECT EVERY PICKUP ON A LEVEL
WATCH THE ALIEN BREED PROLOGUE
COMPLETE ALIEN BREED LEVEL 2 WITHOUT FIRING YOUR WEAPON
REACH AN EXIT DECK LIFT WITH 1 SECOND REMAINING
COMPLETE A LEVEL USING NO KEYS
FLAME 1000 ALIENS
KILL 100 ALIENS
KILL 10 ALIENS
MAKE YOUR FIRST KILL