Grim Idle

adding just one skill point to Dexterity unlocks the Hunter ability. Spend 1 more skill point on this to give yourself a 50% chance of spawning a firefly with each critical hit. This will allow you to pop this one that much quicker.

A much quicker way than waiting to get a critical and clicking on firefly or wasting points on dexterity is to spend the points on bloodthirstiness and rage of darkness in Strength. Then at full energy, initiate rage of darkness(right on d-pad then x). This accelerates clicking to 10 times per second (all over screen). You’ll have the firefly’s, bats, and all the rubies you need to finish this achievement and the other 9 in no time at all. See