Asteroids: Recharged

There's a chance you'll unlock this in Arcade Mode depending on what upgrades you get from the power-up UFOs, but you can also easily get this on the 2nd Challenge level, "Final Burst". This Challenge requires you to kill 100 Small Asteroids, but will start you off with a handful of Large/Medium Asteroids that you need to break apart first. The main two upgrades that will drop in this challenge are the triple shot and the x7 shot, both of which have a pretty decent range of fire. When you don't have an upgrade active, spend some time breaking apart the larger Asteroids so only the smaller Asteroids are left floating about. When you get an upgrade, you'll be able to take out all of the little ones in one go, givng you well more than the 20 required for this trophy. Once you've killed 20 enemies in about a 5-second span, the trophy will unlock.