We Are All Mad Here
Once an ordinary woodman of flesh and blood named Nick Chopper, the Tin Woodman's story is a sad one. His beloved axe was enchanted by a wicked witch in order to keep him from his other true love (it's a long story, but suffice it to say that witches who are wicked do wicked things). His beloved axe turned on Nick Chopper, taking off one limb after another. A tinsmith kindly replaced Nick's missing body parts (except his heart) with tin prosthetics, but eventually nothing was left of the original human and he became the Tin Woodman.
Note that the Tin Woodman will never tell you this story himself, for he has no heart and seeks only revenge: revenge upon the witch who cursed him, upon the tinsmith who did not replace his heart, upon the rain that rusts him. Someday, he will find all the original parts of himself, no matter who they belong to currently, so that he can return to his original form.
Motive: Revenge, find his original body parts
Environment: Anywhere
Health: 21
Damage Inflicted: Moderate wound (4 points)
Armor: 4
Movement: Short; immediate if rusted
Modifications: Speed defense as level 5 due to rust
Combat: Inflicts 7 points of damage with his enchanted axe.
Level 7
Effect: inflicts a moderate wound (7 points); can be activated to move a long distance away from the wielder and attack a foe as an action.
Depletion: 1 in 1d20 (check each activation)
Interaction: The Tin Woodman is singularly focused, and cares only about clues that lead to revenge or his original body parts. He does not eat, drink, or sleep, and often comes across as frantic and frenzied.
Use: The PCs are hunting the same foe that the Tin Woodman is, and either they join together, or the Tin Woodman tries to prevent them from reaching the foe before he does.
Loot: Enchanted axe
GM Intrusion: A character's weapon gets caught in the Tin Woodman's metal body, pulling the weapon out of their hands.