Samus And Chief

Depends on which alien from metroid we're talking about for metroid.

Ing: Not as bad as the Flood for "mutating beyond recognition", but you turn purple, get a goopie hide and gain a few purple horns or tenticles.
Metroids: just om nom you.
X-parasites: First they kill their prey, copy it perfectly, and only if threated or critically injured will it mutate beyond recognition. otherwise has a lot of flood-like qualities.
Phazon: turns you blue over time, and you either get phazon blue clear warts, or crystally hide like qualities.