Lightning RingG 5

This DOES NOT have to be done during a single run.

When:
Anytime from the start of the game.

Method:
Most of the enemies killed will leave behind small gems. Blue ones are of the lowest value, then green, then red, and very occasionally you'll get even more coloured ones.

These gems are your experience - collect them to make killing easier! Kill a total of 5000 enemies across your games (can easily be done in one) and you'll unlock the Lightning Ring.

Achievement unlocked!