Land can’t enter the battlefield, so an effect that “puts a land onto the battlefield” won’t do anything, and the land will stay where it is.

If you cast a spell or activate an ability that lets you put a land onto the battlefield, the effect fails. You’ll still do everything else the spell or ability tells you to do, such as shuffle the library.

In Two-Headed Giant, triggers only once per upkeep, not once for each player.

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.