Very interesting design, evoking a similar feeling to that of The Last King. Corpse Dweller basically turns Humanoid enemies (like Ghoul Minion) into time bombs, requiring you to clear them from the board before they explode into this 3/5/4 2D/1H behemoth. However, doing so will require you to use actions and potentially other resources, such as charges, ammo, or skills, things which you will be sorely needing later on, and Corpse Dweller, unlike the guests in The Last King, isn't guaranteed to detonate. All of this forces you to consider whether you should kill that Ghoul Minion now and (assuming your source of 2 damage isn't renewable) definitely have fewer resources available to deal with the other big bosses or simply evade it and potentially have to spend more resources later to deal with the Dweller.
Alternatively, Player 1 could draw Catacombs Docent, promptly followed by Player 2 drawing the Corpse Dweller, at which point there aren't any mind games to play, but even then, at arguably its lowest point, Corpse Dweller still isn't a bad card; yes, it is a 3/5/4 2D/1H enemy, but that was all that was revealed that turn, giving you more breathing room to take care of it.
All in all, very well-done card. Add in the Return To's fix of making it unable to discard The Man in the Pallid Mask, and it's almost perfect. 10/10, would blow up Tommy Malloy again.