gave Susie a mushy valentine
Nope. Try again.
In their reality, it was duplicate of Calvin who did that.
Interestingly, it didn't happen in Susie's reality either: Calvin gave her a sarcastic
valentine with the same words.
See
Attack of the Deranged Mutant Killer Monster Snow Goons
(also reprinted in
Calvin and Hobbes Tenth Anniversary
).
Artwork © Watterson/UPS; click for notice.