This enemy is similar to Gory Groom, except with more health, less damage and fewer knockbacks. He also gains the ability to warp your cats. With his rapid attack rate, he can break through your defenses easily.
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.
Incidentally, all three were introduced in Lucky Ticket G events.
Due to a bug in the Version 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 portmanteau of "gorilla" and "William".