WMG / The Room (Mobile Game)

The Null doesn't actually absorb souls.

What it feeds on/absorbs is insight: that flash of sudden understanding that comes from figuring things out. Hence, its inculcation of puzzle-obsessions in those who fall under its sway and its spontaneous creation of puzzles-within-puzzles-within-puzzles wherever it's being stored, investigated, or is messing with the boundaries of reality.