I noticed a couple of errors in Mike's promotion to Undead Avenger. After you put him in the salt, he pops out and says "What don't I feel better?" in the dialogue box, while the voice actor says "Why don't I feel better?" so I'm guessing that it's a typo.
And also, in the tower in the Lake of the Rising Sun, when I went to fight the Moo Manchu Thugs, Mike did not appear in the battle. Was this intended?