As a category, (???2)Grpd(-2)\Grpd is a monoidal category in a unique way, and a groupoid enriched over this should be (at least up to equivalence) a (???1)(-1)-groupoid, which is a truth value; and indeed, a groupoid enriched over (???2)Grpd(-2)\Grpd is a groupoid in which any two objects are isomorphic in a unique way, which is equivalent to a truth value.