It's all in the description of the achievement. Find a character you enjoy and just work on getting some of the evolved weapon achievements, and this one will pop through normal game play.
After playing the game awhile you will wonder why you ever thought this was a challenge when you started, so just be patient.
A fully evolved pentagram is a very useful tool if you are struggling to unlock the levels coffin achievement. Although a level 7 or so Pentagram is plenty powerful enough to help with this on levels 1 & 2.