Here is the full list of all 28 MultiVersus achievements.
Play 500 matches in a party
Get 100 Double Ringouts
Play 100 matches in a party
Get 200 Ringouts with a Projectile
Get 100 Ringouts using your spike
Win 300 matchmade games
Get 50 Ringouts using your spike
Play 25 matches in a party
Accept 100 rematches
Get 25 Double Ringouts
Get 50 Ringouts with a Projectile
Win 100 matchmade games
Get 20 Ringouts with a Projectile
Give out 100 Toasts to other players
Get 10 Double Ringouts
Get 10 Ringouts using your spike
Get 10 low-damage Ringouts
Get 100 Ringouts
Get 10 Ringouts using the bottom of the Blast Zone
Get 10 Ringouts using the left-side of the Blast Zone
Get 50 Ringouts
Get 10 Ringouts using the right-side of the Blast Zone
Get 30 Ringouts
Give out 10 Toasts to other players
Win 10 matchmade games
Give out 5 Toasts to other players
Get 10 Ringouts using the top of the Blast Zone
Play 1 matchmade game