Gilligan is a special monster found at the Castaways' Fortress.
Breaks your items, Range 1
Kinetic, Damage 10-15, Range 1
It's possible to kill Gilligan from a distance by using ranged weapons, grenades, etc. The easiest way, though, is to retrieve the Skipper's Hat and 'u'se it as a weapon. If you hit Gilligan with the Skipper's hat, Gilligan is unable to use his special attack, and will simply bite you for ~10 damage.
Gilligan holds the Keptibora Serum.