4 Oct 2004
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.
4 Oct 2004
If you have less than 4 creatures, you do not partially sacrifice. You pay 4 creatures or none.
4 Oct 2004
The sacrifice is done as a triggered ability just after it enters. It is not done on casting.