Rtas 'Vadum in crashed Flood ship

The Half-Jaw in crashed Flood ship easter egg can be found on the level Floodgate.

When you jump down the hole to get into the Flood ship that crashed, there will be a few dead Ultra Elites lying around. Sometimes one or more will have Rtas Vadum's (Half-Jaw) face. However, it is the old model from Halo 2. You can get it infected too if you push it down the hole and release some Infection Forms, though when he turns into a Flood Combat Form, his armor changes to the default blue like most Flood.