The mythical creature is the prefix, and the Peanuts character is the suffix.
Mythical Creature:
Unicorn: Silver
Pegasus: Eagle
Dragon: Blaze
Phoenix: Flame
Mermaid/Merman: Trout
Centaur: Birch
Fairy: Dove
Troll: Red
Gnome: Leaf
Leprechaun: Clover
Elf: Bramble
Peanuts Character:
Snoopy: foot
Charlie Brown: stripe
Lucy: pelt
Peppermint Patty: fur
Linus: tail
Shroeder: breeze
Marcie: feather
Sally: heart
Pigpen: wing
Franklin: pool