When Hecatomb enters, sacrifice Hecatomb unless you sacrifice four creatures. Tap an untapped Swamp you control: Hecatomb deals 1 damage to any target.
2004-10-04
If you have less than 4 creatures, you do not partially sacrifice. You pay 4 creatures or none.
2004-10-04
The sacrifice is done as a triggered ability just after it enters. It is not done on casting.
2004-10-04
You choose whether to sacrifice creatures or not on resolution. If not, then you sacrifice Hecatomb. You can choose to not sacrifice creatures if you no longer control this card on resolution.