"For The Group!" (often said as #forthegroup) is a gag created by the Creatures in the TreeTopia/TreeBoot Series but is mostly used by Seamus, James and Aleks, making fun of Sly. Jordan, in Sly's Surprise Special, has also mocked the gag in his pent-up rage towards Sly and his tyranny by saying, "#forthegroup? Are you kidding me with that?"
Throughout the series, "For the group" is said when one finds something valuable or deemed usable by the entire group. It's also used for mocking someone if they keep valuable items for themselves. It has also been a quick joke by Immortal that "If I find Coal, it's for the group, If I find Iron, for the group. If I find Diamond, it's for me", mocking how Sly kept all the diamonds for himself.
Sp00n also used the term multiple times in Saints Row 4, notably when Nova was unable to finish a mission. This is probably because Sp00n edited the first few sessions of TreeTopia. It has also been used in Skygrid by Immortal, Sly and Kevin.