to get this you need the following summons
dragon egg
friendly ghost
magic dagger
second magic dagger
magic scythe
electro bug
magic lens
seismic ward from the rune shop on the character select screen
I recommend you do this as shana so you can reroll if you don't get any of these or an upgrade that gets you closer to one of these, also play on darkness 8 or below for maximum choices in upgrading.
i've also heard that shana can get it by tripling a summon after killing a boss, but this is uncomfirmed and inconsistent. going over 8 with this does not stop you from getting the achievement though, so try it if you get the chance.