This enemy is similar to Gory Groom, except with more health, less damage and less knockbacks. He also gains the ability to Warp your cats. With his fast attack rate, he can destroy your defenses easily.
Cat Units with the Freeze ability (Surfer Cat, Balalan Pasalan, Akira, etc.) can do wonders as they can stop him from destroying your front lines and warping them back. Warp Blockers can not be Warped and therefore prevent Gorilliam from pushing through your lines, or at least slow him down. When Gorilliam is given higher buffs in later stages, Warp Blockers start to become useless, as his damage is enough to kill or knockback most meatshields in 1 hit, in which case it is best to just use Psychocat or Surfer Cat to stop him from moving forward. Anti-Alien Cats with Massive Damage/Insane Damage (except for Chill Cat because of poor range) could also help to make quick work of Gorilliam.
Due to a bug during the 10.6 Update, Gorilliam’s name in French was “Gory Alien.” Alien is his trait, but the word alien appears nowhere in his name, rather being a combination of “Gory” and “William.”