The Afterparty is a Legends of Idleon quest: 2 rewards. Defeat monsters with other party members around you.

The Afterparty | Idleon Toolbox

Defeat monsters with other party members around you.

The_Afterparty

Hold to open! Contains a random Falloween Event goodie, including 3 limited time Monster Masks, check Patch Notes in Discord or Steam for info! Also, if you open 500 Treats you'll get the Falloween Event NAMETAG!

Falloween_Treat

Hold down to instantly get anywhere from 20 minutes to 12 hours of AFK time!