Yigs have greater phenotypic variation than humans, which is a common feature of relatively new races. Most yigs aren’t the human-like creatures we’ve seen from the inn, but bent little “goblins”–the result of Tamantha causing a slow diminishing of each subsequent race’s baseline potency, from the immortal and near-indestructible chuni (Lyca isn’t anything special; she was just some college student working the equivalent of the Peace Corps when she got tangled up in events) down to the wyrds and Ulenites, then the humans (and a few contemporaneous races), and finally the yigs and the very newest races.

Vish has a chart of all this somewhere, probably.