Revealing mistake: Throughout the scene where Eddie is in Toontown, you can find many shots where Eddie is slightly transparent, with the background showing through him. One example of this is when Eddie looks inside the yellow car, and you can see the car through his body. (01:10:57)
Audio problem: After Judge Doom gets sprayed by the Dip spraying machine, he stands up and says, "Oh no!" but his mouth stays shut. (01:31:47)
Revealing mistake: When Judge Doom gets sprayed by the Dip spraying machine, stunt cables attached to him are visible, pulling him backwards. Christopher Lloyd also seems to have been replaced with a dummy. (01:31:22)
Answer: Valiant also shares his name with Arthurian comic strip hero Prince Valiant, who wields a singing sword, Flamberge.