https://www.youtube.com/watch?v=swA-IcceC20
Opened Jumbo Spectral Pack > 8 cards in hand > Immolate to destroy 5 > 3 cards remaining (can still use Grim) > Hanged Man to destroy 2 > 1 card remaining > can no longer use Grim
If this is not a bug please let me know! But from what it seems I should be able to use Grim and other Destroy 1 random card in your hand spectral cards