I'm going to have a GREAT TIME!
They are all 1.5" in size not including the keyring.
BONUS: If you order both UnderFell Sans and UnderFell Papyrus keychains in a combo, you get one of each as a button for free (sparkle or normal versions depending on which set you order). A $4 value, free~
UnderFell created by the Tumblr Undertale AU community
Not officially licensed merchandise, but some really cool fan art!