Each player loses X life, discards X cards, sacrifices X creatures, then sacrifices X lands.
The swarm's million wings stir the foulest of breezes.
Official Rulings for Death Cloud
6/7/2013 : If you control a permanent that's a creature and a land, and you choose to sacrifice it as you sacrifice creatures, it won't be on the battlefield when you sacrifice lands. You can't sacrifice it again.
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