Out of Character
Backtagging:
Yes. I tend to want to wrap up game threads within roughly a month, though, and prefer to wrap threads before starting new ones with the same character.
Fourthwall:
Yes. The likelihood of Castiel understanding is... debatable.
Offlimits:
"on screen" domestic/sexual abuse, pregnancy related body horror
Threadhopping:
Yes if it makes sense. In general I'd prefer if you asked first, though.
Handwaving:
Yes, for non-essential developments
Powers / Abilites
Smiting:
Castiel can smite regular tier demons and monsters, burning them out of existence with divine power. He usually does this via touch with demons, but against low powered monsters has been seen releasing a lot of energy in a blast of white light to smite them without touching them.
Immortality/Invulnerability
Angels are to varying extents impervious to or unbothered by damage to their vessels, and can maintain the state of their vessel as they took it, requiring no sleep, nourishment or regular human "maintenance" of any physical aspects, as well as regenerate damage to the body nearly instantaneously (physical wounds as well as damage to the clothing). Physical damage to the vessel is implied to hurt angels to varying degrees based on their power level/level of impact. Castiel reacts to being shot with a shotgun with annoyance, is unbothered by being stabbed, and can take a physical beating from a non-powered-human without any issues (humans with superhuman strengths/other creatures can still superficially wound him, though).
Healing (Others/Himself)
Castiel can heal any physical damage to a body, including his own, as well as detect and purge some natural infections/illnesses, eradicate long-term disabilities, and even reattach limbs/appendages shortly after their loss/removal.
Resurrection:
Castiel can resurrect the recently deceased and bring them back to life. This costs him a tremenous amount of power when not backed by Heaven itself.
Flying/Teleportation:
Angels have wings. However, in Supernatural, the wings aren't typically shown to be physical. They CAN be, because in a later season we know that an angel feather was used as a spell ingredient, and we see angels wrapping those shadows around themselves/others to shield against magical damage. However, it seems angels tend to keep their wings cloaked/invisible, though when an angel powers up, the shadows of those wings can be seen behind them. Their flight is much more akin to telportation across vast distances and to any unwarded location of their choosing, though the instantaneous moving through space is accompanied by the rustling of feathers, meaning wings are for sure being flapped.
Mind Reading:
Castiel can skim surface thoughts without much effort to gain deeper insight into people, as well as actively read their minds with more effort, and perceive the state of their soul to an extent. Through this, Castiel can sense/detect the location of humans who are not warded from his senses. He also seems to gain an understand of animal minds, as he can tell when dogs are upset, is seen interrogating a cat, and can detect the messages in a honeybee's flight pattern.
Clairsentience:
Castiel can see the true "face" of angels, demons and leviathan, and see through the Veil, as in he can see creatures invisible to the human eye like ghosts and reapers. This in combination with his psychic abilities can lead him to detect the true nature of a creature.
Mind/Memory Manipulation:
Castiel has been shown to be able to manipulate and erase memories. He only ever does it in canon upon other people's request, and even though he can do it, doesn't use it on his friends even when doing so would clearly benefit him. Castiel respects free will too much for that. He has used it under specific circumstances at the behest of others. In addition we also see him manipulate other character's ability to perceive him by cloaking himself from them - physically present but unseen. In one instance, he touches a security guard and alters his mind to be unable to perceive any other person in the room, even though they're all physically present.
Sleep/Dream Manipulation & Dreamwalking:
With a touch, Castiel can make people and certain low-powered creatures fall into a deep slumber.
Castiel and other angels have been shown to be able to enter the dreams of humans to communicate with them. And see what they're dreaming of. Additionally, Castiel is able to manipulate sleeping humans to prevent them from experiencing nightmares, or even to sleep more deeply than they naturally would to prevent them from waking prematurely.
Telekinesis:
Castiel isn't seen to use this too often, but he does have some level of ability to blast open doors, move objects, shut off car alarms with the wave of a hand.
Super Strength & Endurance:
Angels are far stronger than humans and even most demons, and more resilient, shown to lift objects impossibly heavy for humans, or punch one another through walls.
True Form/Vessel:
Castiel is possessing someone else's body. That someone else is Jimmy Novak, who died and passed on to Heaven after Castiel was killed for the first time. The body has since been destroyed a few more times, and been restored, sparing Castiel from having to possess a new vessel. Angels can only possess people if they consent to it (though manipulation to gain said consent is apparently allowed). The experience is typically not pleasant to downright tortuous for the host as long as the angel is in control, but the angel can be dormant/unnoticed and leave the host in control. Theoretically, with consent, Castiel could possess the bodies of other characters.
Additionally of note is the fact that few humans are able to perceive an angel's true form. Despite his warnings, a psychic uses her abilities to see Castiel once, and it burns out her eyes. Longer exposure results in death. The true voice of an angel, similarly, can damage ear drums, shake buildings and break glass. Castiel once claims that his true form is "the size of the Chrysler Building." Suffice to say: No one wants to see him forced out of his vessel.
Content Warnings
Religion/Blasphemy
Castiel is an angel of the Lord. His faith has been broken, and he's invested it away from his Father. Heaven in Supernatural is a flawed, corrupt system. In Supernatural mythology, God not only exists, he's also created other religions and deities. His views towards religion and faith might come off jaded, especially towards highly religious characters.
Torture, Brainwashing
In his past, Castiel has canonically been tortured and undergone heavy brainwashing and altering of his own mind and memories at the hand of Heaven, as well as regularly lost his mind and/or autonomy to other outside influences. This heavily shapes who he is, and might regularly crop up in his narrative.
Suicidal Ideation, Self-Loathing, PTSD, Self-Sacrifical tendencies
Time and time again, Castiel has shown to believe himself chasing redemption he doesn't believe he'll ever fully achieve. He carries within him heavy guilt, and often believes that he deserves death, that he is useless, expendable and best serves others by sacrificing himself.
Shipping
Canon OTP
Dean Winchester
Other Canon Ships
Meg, Sam, Balthazar, Hannah
NoTP
Chuck/God, Jack Kline, Claire Novak, Metatron, Dick Roman, Jimmy Novak
Other
For Memes: Other Cast Mates if discussed, open to cross canon, assumed CR, OCs, AU. Feel free to approach
Notes on Shipping
Most of these are for memes. Castiel is canonically in love with Dean Winchester, and while he has been shown to express other less deeply running romantic interests (mainly Meg and Hannah), he is slow to develop feelings outside of Dean, and will prioritize Dean above all others. In a game setting adhering to his canon interests, it would be an extremely long time before he'd feel for someone like he does for Dean. For memes, I'm willing to play a bit fast and loose with this, but for games, consider him pretty much taken even if not currently in a romantic relationship with Dean himself.