Grub can be found with his best friend, Yenna, in Rivington during Act 3. If Grub and Yenna are allowed, they can become Camp Followers and will remain at the party's Camp. Grub is shy and a bit anxious, and his trust is only gained by ignoring him. He appears to have some manner of sixth sense regarding the danger Yenna is potentially in, telling the player character that they should be helping her if using Speak with Animals.
Grub will be killed if Orin the Red kidnaps Yenna. This can be prevented by leaving an alternative companion at camp (Lae'zel, Gale or Halsin/Minthara).
If Yenna is killed, Grub will dutifully sit by her side and mournfully meow.
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Grub's model.