Good-Fortune Unicorn is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Whenever another creature you control enters, put a +1/+1 counter on that creature.

Complete guide

Good-Fortune Unicorn is a charming addition to Selesnya decks that focuses on making your army bigger as it grows. This creature provides immediate value simply by existing on the battlefield as your other threats arrive. By automating the growth of your creatures, it ensures every new arrival is a bigger threat than it would be on its own.

A Stampede of Counters

Good-Fortune Unicorn has a triggered ability that triggers whenever another creature enters the battlefield under your control. It does not matter if that creature was cast as a spell, put onto the battlefield by an effect, or created as a token. As long as it is a creature and you control it, the Unicorn will try to place a +1/+1 counter on it.

The Timing of Growth

When a creature enters the battlefield, the Unicorn's ability is put onto the stack. This happens after the creature is already on the battlefield. Players can respond to this trigger before the counter is actually placed. If the new creature is destroyed in response to the trigger, the trigger will still resolve, but it will fail to put a counter on the creature because that creature is no longer on the battlefield.

Common Mistakes

It is important to remember that Good-Fortune Unicorn says 'another creature.' This means the Unicorn does not put a +1/+1 counter on itself when it enters the battlefield. Additionally, if multiple creatures enter at the same time (for example, from a mass resurrection spell), the Unicorn will trigger once for each of those creatures, and you will put a counter on each of them.

When to Play It

You should aim to play Good-Fortune Unicorn early in the game, ideally on turn three. This allows you to maximize the number of creatures that benefit from its ability. It is particularly effective in decks that use many small creatures or tokens to overwhelm the opponent, turning a 1/1 token into a more respectable 2/2 threat immediately.

Interaction examples

Automated Value

Solemn Simulacrum

With Good-Fortune Unicorn on the battlefield, you cast Solemn Simulacrum. When the Simulacrum enters, two triggers go on the stack: the Unicorn's counter ability and the Simulacrum's land-search ability. You can order them however you like. Regardless of the order, the Simulacrum will receive a +1/+1 counter, making it a 3/3 creature while you search for your basic land.

Strategic Sacrificing

Sakura-Tribe Elder

If you play Sakura-Tribe Elder while Good-Fortune Unicorn is out, the Unicorn's trigger goes on the stack. If you choose to sacrifice the Elder in response to the trigger to search for a land, the Elder moves to the graveyard before the trigger resolves. When the trigger finally resolves, the Elder is gone, so no counter is placed, but you still get your land.

Guide written with AI from the official text and rulings. Official English text prevails.