Players can't play lands.
Lands can't enter the battlefield.
At the beginning of each upkeep, any player may sacrifice two lands or have Worms of the Earth deal 5 damage to that player. If a player does either, destroy Worms of the Earth.
If a permanent spell tries to enter the battlefield as a land during its resolution (for instance, a Clone entering the battlefield as a copy of a Dryad Arbor or an animated Mutavault), it is put into its owner’s graveyard instead of entering the battlefield. It never enters the battlefield, so abilities that would have triggered on it entering the battlefield won’t trigger.