Completing Group Hug unlocks the "Organic Goblet" Etheria Crystal skin.
As of patch 7.16, the counterpart hero classes now also count towards this achievement.
Good Student - Completed the Tutorial. You deserve a cookie!
Pupil - Reached Hero Level 10
Veteran - Reached Hero Level 30
Defender of Etheria - Reached Hero Level 70
Group Hug - Raised a Hero of each type to Level 70