The release date on mutations for players has yet to be announced and confirmed, and will not be coming out any time soon (supposedly longer than 8 months). Take the information on this page with a grain of salt and not to be taken as fact.
According to the game's trello, a player would be able mutate their magic at level 300(?). Contrary to what some may think, mutations are not a combination of the First and Second Mind, instead they are both completely independent when mutating.
The First and Second Mind Magic may mutate at Level 300(?) and Level [#] respectively. The Third Mind Magic cannot mutate at all. If the player wishes so, they may choose to not mutate their magic to learn additional moves for their source magics.
The chart shown above is mostly outdated, and there is going to be a new chart that comes out a few weeks before mutations come out.
Click here for the creator's early words about mutations on this trello page.
Verdies, Angry Pirate Captain - Plasma Magic
Theos, The War Phoenix - Sun Magic and Phoenix Magic