Animagus/Werewolf Headcanons

Animagi

• Marks on an Animagus' human form transfer over to their animal form
• Ex. Sirius and his tattoos
• Sirius' tattoos come up as white markings on Padfoot's fur
• Certain scars would transfer between forms - specifically scars caused/infected by magic.
• Ex. Harry's scars
• The Lightning Bolt - it's a curse scar, and it's full of magic
• The Basilisk Bite - Basilisks are magical creatures, then you add Fawkes' tears and that's a ton of magic imbued into that scar
• The Acromantuala Bite - Magical spiders, 'nough said. 
• The Locket - Horcruxes are pure magic and soul, which would burn Harry's own, leaving a soul-deep scar. 

Werewolves

• Marks on a werewolf's wolf-form transfer over to their human form
• Ex. the scars on Remus
• Being a werewolf is like having Dissociative Identity Disorder.
• The trauma of the Bite creates 'another' personality - the Wolf. 
• The Wolf causes Black-outs on the Full Moon, much like DID.
• Often memory loss accompanies the Moon.