Is it possible to play Marrow Shards in the second main phase after combat is completed? Marrow Shards says:
Marrow Shards deals 1 damage to each attacking creature.
My opponent played this card only to do the same damage with his Rage Extractor. I think he is allowed to do this, because there are no prerequisites like a valid target or something like that. If this is really possible, what happens to creatures that attacked in the combat phase? Do they still count as attacking creatures and so take damage from the spell?