Here is the full list of all 10 Magnet Knights (EU) trophies - there are 5 bronze, 4 silver and 1 gold.
Win every round in a tournament
Win a tournament without taking any damage
Be warped out of a game
Collect 50 Power-ups
Magnetise a knight 100 times
Use the Mighty Hammer 100 times
Win a tournament without attacking anyone
Win a tournament using only the bow
Win a tournament with the most attacks
Get all the Gold Trophies in "Training Mode"