TK’s Guardian and Manipulator Forms  
Base by ElementBases  
TK’s other forms, her later Guardian form, and her Manipulator form.  
A little about the Guardian mark:  
TK’s cutie mark isn’t actually a star with a water droplet, it’s just a water droplet. The Guardian mark is passed down to a new guardian and a pony’s cutie mark goes to the center of it. TK wasn’t the one who was supposed to get it either. It was actually supposed to go to her daughter but the Guardian before her turned evil and the guardian before her took it away, passed it on early, and locked her away. There have been 4 guardians so far, TK being the 4th. The creator(unknown gender or species), a unicorn stallion, an earth pony mare, and TK(born a pegasus). It does turn it’s user into an alicorn. It also has a way of telling the heart of its user, if the star is white then they have good in them, doesn’t mean they are “good” like with the Manipulator. If it is black, the pony is troubled and has a dark heart. The Guardian and TK. But doesn’t mean that they are “evil”.  
The Guardian mark gives a pony guardianship of all magic, they have to protect it and use it to keep all magic in balance. When a pony uses a certain kind of magic the guardian mark can change. If she uses Twilight’s magic then the water droplet will turn into Twilight’s cutie mark, but the star stays the same. But just because the pony has access to others magic doesn’t mean that it’s any easier to control. Might seem like they can use any magic they want to at any time, nope! They have to learn every magic just like a normal pony, they just learn a lot more of it. The Guardian is the most powerful creature. Not just in Equestria.  
How can one pony/creature handle all that magic?!  
They can’t. The Guardian mark has all the magic, not the pony. And if removed (the user can remove it at will but only temporary) can stay off for a while and the user doesn’t have it’s magic or alicorn form. Just a normal pony. TK didn’t want the responsibility of it and cracked turning herself into the Manipulator. (But was reformed back to her normal self)  
What if they decide to remove it and don’t put it back?  
They can’t. The moment they decide to keep it off permanently it’s passed on and if they have had it too long age, disease, etc catch up and kill them. The only reason the third user didn’t die was because she hadn’t had it that long and was supposed to have it much longer. TK’s daughter would have been an adult, TK was a 6 year of old filly when she got it. But with the first two they were killed when they passed it on. But since TK’s daughter wasn’t alive it went to her instead.