New concepts of Merlin’s magical abilities I would love to see in fanfics and headcanons:
1. Any person who drinks a bit of Merlin’s blood gains the ability to use magic. The show states magic is learned, people study for years to learn how to practice magic, only some people are born with a natural aptitude towards it. By drinking Merlin’s blood anyone can suddenly use magic, even if they never studied it before, but they’ll still have to learn how to control it.
2. Merlin can’t die by drowning, he can breathe under water for a longer time than an average human, but if water gets inside his lungs and he can’t breathe he will go into a dormant state until his lungs are cleared again, it could be hours, days or years (or centuries), he will always regain consciousness once he can breathe again.
3. Merlin can only be killed by weapons forged by magic or by the complete destruction of his body (like burning), if there’s even the smallest possibility of his body being healed, it will heal. Merlin does die from other common factors, but he comes back again. For example, if he’s given a deadly poison or stabbed by a common weapon, his heart will stop and he’ll die, then in a few minutes his heart will restart and he’ll live again. But every time he dies and revives, he’s a little less himself, like some parts are chipped away.
4. Merlin can build resistance to poison. Once he comes in contact with a certain poison he’ll become immune to it’s effects. Based on the previous concept, once Merlin learns he won’t permanently die from poison, he starts experimenting with various ones, his heart stops but he eventually comes back to life and heals from it’s effects, from then on he’ll be unaffected by it if he ever comes in contact with the poison again.
5. Merlin can enter the mind of animals at will, perceive the world through their senses and control their actions (like warging from ASOIAF). For example, while camping outside, he could enter the mind of a owl during the night and keep watch through it’s eyes while his actual body rests.
If anyone has other concepts and headcanons about Merlin’s magic and/or immortality I would love to know them too! Also english is not my first language, sorry if there’s any mistakes.