Oh yeah, I'm not planning on having monsters be fine with him. My PCs are fairly predictable in a good way so they'll soon start collecting the crystals to prevent my cult from doing so (who has no idea about what is going on).

From there, everything will be trying to prevent this, the remaining crystals are mostly sealed away in veritable death traps guarded by monsters and traps.

For those crystals that aren't sealed away the PCs will still have to do a lot to get them. One particlar planned example is a hermit just outside a distant village finds one. Getting news of this the PCs will go to him and find him in his cottage, injured, with the crystal and babbling "Don't let it in" before dying dramatically.

From there they deal with a Nightwalker who works on converting the whole village into Bodaks to wrestle the crystal from the PCs and take it to the shadowrealm.