Merfolk Branchwalker
Oracle Text
When Merfolk Branchwalker enters the battlefield, it explores. (Reveal the top card of your library. Put that card into your hand if it's a land. Otherwise, put a +1/+1 counter on this creature, then put the card back or put it into your graveyard.)
Card Rulings
1/19/2018 Once an ability that causes a creature to explore begins to resolve, no player may take any other actions until it’s done. Notably, opponents can’t try to remove the exploring creature after you reveal a nonland card but before it receives a counter.
1/19/2018 If no card is revealed, most likely because that player’s library is empty, the exploring creature receives a +1/+1 counter.
1/19/2018 If a resolving spell or ability instructs a specific creature to explore but that creature has left the battlefield, the creature still explores. If you reveal a nonland card this way, you won’t put a +1/+1 counter on anything, but you may put the revealed card into your graveyard. Effects that trigger “whenever a creature you control explores” trigger if appropriate.
explore is a pretty good keyword I'd love to see be used semi-regularly. Card flow/land consistency mechanic that is also creature buff/counters is interesting space. the GU merfolk have a nice Simic vibe going with the +1/+1 counter synergy that reminds me of graft synergies, which is partially supported by explore.
In the early game, it help you dig for lands and dump late-game cards. In the late game you have less lands in your deck, so you're probably just going to get a beatstick with a bit of card filtering.