Ash, Party Crasher

Haste
Celebration — Whenever Ash, Party Crasher attacks, if two or more nonland permanents entered the battlefield under your control this turn, put a +1/+1 counter on Ash.

Lady of Laughter

Flying
Celebration — At the beginning of your end step, if two or more nonland permanents entered the battlefield under your control this turn, draw a card.

Belligerent of the Ball

Celebration — At the beginning of combat on your turn, if two or more nonland permanents entered the battlefield under your control this turn, target creature you control gets +1/+0 and gains menace until end of turn. (It can't be blocked except by two or more creatures.)

Pests of Honor

Celebration — At the beginning of combat on your turn, if two or more nonland permanents entered the battlefield under your control this turn, put a +1/+1 counter on Pests of Honor.

Grand Ball Guest

Celebration — Grand Ball Guest gets +1/+1 and has trample as long as two or more nonland permanents entered the battlefield under your control this turn.

Goddric, Cloaked Reveler

Haste
Celebration — As long as two or more nonland permanents entered the battlefield under your control this turn, Goddric, Cloaked Reveler is a Dragon with base power and toughness 4/4, flying, and "{R}: Dragons you control get +1/+0 until end of turn." (It loses all other creature types.)

Bespoke Battlegarb

Equipped creature gets +2/+0.
Celebration — At the beginning of combat on your turn, if two or more nonland permanents entered the battlefield under your control this turn, attach Bespoke Battlegarb to up to one target creature you control.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)

Gallant Pie-Wielder

First strike
Celebration — Gallant Pie-Wielder has double strike as long as two or more nonland permanents entered the battlefield under your control this turn.

Raging Battle Mouse

The second spell you cast each turn costs {1} less to cast.
Celebration — At the beginning of combat on your turn, if two or more nonland permanents entered the battlefield under your control this turn, target creature you control gets +1/+1 until end of turn.

Armory Mice

Celebration — Armory Mice gets +0/+2 as long as two or more nonland permanents entered the battlefield under your control this turn.

Tuinvale Guide

Flying
Celebration — Tuinvale Guide gets +1/+0 and has lifelink as long as two or more nonland permanents entered the battlefield under your control this turn.