If you play a card this way, it leaves exile and becomes a new object. If it returns to exile later in the turn, you can't play it again.

You must follow the normal timing permissions and restrictions for the exiled card. If it's a land, you can't play it unless you have land plays available.

If you play the card in response to the end step triggered ability, that card won't be put into your graveyard and won't be counted when determining how much damage to deal.

In a Two-Headed Giant game, the end step triggered ability causes the opposing team to lose 2 life for each card put into its owner's graveyard.

You'll still pay all costs for a spell cast this way, including additional costs. You may also pay alternative costs if any are available.

If Valakut Exploration leaves the battlefield, any cards exiled with it remain exiled and can be played. The end step triggered ability won't trigger, and the cards won't be put into their owner's graveyard.

Whenever a land you control enters, each landfall ability of the permanents you control will trigger. You can put them   on the stack in any order. The last ability you put on the stack will be the first one to resolve (As a result, you can have those abilities resolve in the order of your choosing.).

A landfall ability triggers whenever a land you control enters for any reason. It triggers whenever you play a land, as well as whenever a spell or ability puts a land onto the battlefield under your control.

A landfall ability doesn't trigger if a permanent already on the battlefield becomes a land.