Lutri, Pauper Otter

If you reveal a companion outside the game, for as long as it remains there, you may pay {3} any time you could cast a sorcery (that is, you have priority during your main phase and the stack is empty). Once you do, you put it into your hand and it behaves like any other card you’ve brought into the game. For example, if it’s discarded, countered, or destroyed, put it into your graveyard.

The companion ability has no effect if the card isn’t revealed as your companion at the start of the game, and it creates no restrictions on putting a card with a companion ability into your starting deck. For example, Lutri, Pauper Otter may be in your starting deck even if your starting deck contains cards with silver, gold, orange, and/or purple expansion symbols.

Before shuffling your deck to become your library, you may reveal one card from outside the game to be your companion if your starting deck meets the requirements of the companion ability. You can’t reveal more than one. It remains revealed outside the game as the game begins.

For many playtest cards, you’ll need to make a generous assumption that basic game rules would be updated to allow them to work. The Mystery Booster 2 Playtest Card Notes section (reproduced here in individual Gatherer rulings) provides guidance for fitting these cards into the existing rules structure.

Expansion symbols on playtest background cards don’t count, even if they’re partially visible.

If more than one player wishes to reveal a companion, the starting player does so first, and players proceed in turn order. Once a player has chosen not to reveal a companion, that player can’t change their mind.