Rogue Elephant

When Rogue Elephant enters, sacrifice it unless you sacrifice a Forest.

Tapping at the Window

Look at the top three cards of your library. You may reveal a creature card from among them and put it into your hand. Put the rest into your graveyard.
Flashback {2}{G} (You may cast this card from your graveyard for its flashback cost. Then exile it.)

Adventurous Impulse

Look at the top three cards of your library. You may reveal a creature or land card from among them and put it into your hand. Put the rest on the bottom of your library in any order.

Forest

Rancor

Enchant creature
Enchanted creature gets +2/+0 and has trample.
When Rancor is put into a graveyard from the battlefield, return Rancor to its owner's hand.

Scythe Tiger

Shroud (This creature can't be the target of spells or abilities.)
When Scythe Tiger enters, sacrifice it unless you sacrifice a land.

Llanowar Stalker

Whenever another creature you control enters, Llanowar Stalker gets +1/+0 until end of turn.

Harvest Wurm

When Harvest Wurm enters, sacrifice it unless you return a basic land card from your graveyard to your hand.

Experiment One

Evolve (Whenever a creature you control enters, if that creature has greater power or toughness than this creature, put a +1/+1 counter on this creature.)
Remove two +1/+1 counters from Experiment One: Regenerate Experiment One. (The next time this creature would be destroyed this turn, instead tap it, remove it from combat, and heal all damage on it.)

Borderland Explorer

When Borderland Explorer enters, each player may discard a card. Each player who discarded a card this way may search their library for a basic land card, reveal it, put it into their hand, then shuffle.

Nettle Sentinel

Nettle Sentinel doesn't untap during your untap step.
Whenever you cast a green spell, you may untap Nettle Sentinel.