It That Gets Left Hanging

When It That Gets Left Hanging enters, ask a person outside the game to high-five you. If they won't, It That Gets Left Hanging gains haste until end of turn.

Entirely Normal Armchair

During your turn, if Entirely Normal Armchair is in your hand, you may hide it on the battlefield.
{0}: Return Entirely Normal Armchair to its owner's hand. Only your opponents may activate this ability and only if they see Entirely Normal Armchair.
{2}, Sacrifice Entirely Normal Armchair: Destroy target attacking creature.

Pietra, Crafter of Clowns

Haste
Robots you control get +1/+1.
{R}{W}, {T}, Tell a joke you haven't told this game to someone outside the game: Create a 1/1 white Clown Robot artifact creature token. If that person laughed, the token gains haste until end of turn.

Gimme Five

You gain 1 life for each person who high-fives you in the next thirty seconds. Each player in an Un-game who high-fives you gains 1 life. (Offer high fives. Don't hit people.)