Ensemble Darkhorse: Walter, played by Jim Carrey. Surprisingly a naunced role, because despite being a wild and crazy guy ("Whatever Walter wants, Walter Getz!"), he's a fucked up guy in the 1980's who is hooked on cocaine.
"Funny Aneurysm" Moment: After Peggy Sue returns from her time travels, Charlie said he would cut his right arm off for another chance to reconcile with her. Ronny, Nicolas Cage's character in Moonstruck, is missing a hand due to an accident at the bakery after his fiancée dumped him.
Special Effect Failure: The opening shot through the mirror uses body doubles, and it's done well enough that if you aren't looking you won't notice the "reflection" being out of sync - but is jarring when you do.
Tearjerker: When Peggy gets a call from her grandmother. Anyone who's lost a grandparent will understand her Heroic BSOD and inability to talk to her.