Cryptex

{T}, Collect evidence 3: Add one mana of any color. Put an unlock counter on Cryptex. (To collect evidence 3, exile cards with total mana value 3 or greater from your graveyard.)
Sacrifice Cryptex: Surveil 3, then draw three cards. Activate only if Cryptex has five or more unlock counters on it.

Murders at Karlov Manor Promos

Murders at Karlov Manor

{T}, Collect evidence 3: Add one mana of any color. Put an unlock counter on Cryptex.
Sacrifice Cryptex: Surveil 3, then draw three cards. Activate only if Cryptex has five or more unlock counters on it.

Cryptex’s first ability is a mana ability. It doesn’t use the stack and can’t be responded to.

If you can’t exile enough cards to meet or exceed the required mana value, you can’t choose to collect evidence at all.

Once you’ve announced that you’re casting a spell, players can’t take actions until you’ve finished doing so. Notably, opponents can’t try to remove cards from your graveyard to stop you from collecting evidence.