Hey which is more powerful the Gankyil dragon's master of magic or Riem's heart's desire? Also how does the gankyil dragon fit the theme of eschatolic (end of the world)? I understand with the other two.
So the Gankyil represents transcendence, or the ability to overcome, they are created from Time Lords and similar beings, in this multiverse, they are technically not 'needed' but exist and are a means of a determined being changing an outcome, in essence they represent the possibility of change even in the face of multiversal destruction. They represent hope in a way, hope that never dies and the tenacity to change that which 'cannot' be changed, theoretically.
The Master of Magic Metempiric Ability is considerably more powerful than the Hearts Desire ability, at first blush, but though the two seem similar, the two are very distinct.
Heart's Desire is a snare for Reim to transfer a being's potential into himself, he can create any effect he so chooses but this is usually chosen by the recipient at the time it's used, and his energy is still limited to the parameters of the ability, meaning he cannot use it to just give himself whatever he wants and he must persuade beings to give him their energy without forcing it. It must be freely given but once given their energy is his, no matter how strong they become he is immune to being destroyed by them and can tap into their essence, his ultimate goal is to depose Thychen so he uses this and bides his time hoping to eventually gain enough power to outsmart him and take the Throne.
The Gankyil on the other hand is an extramultiversal entity and outside the parameters of Thychen's creation, it's Master of Magic ability, in fact, taps into the same source energy that Thychen uses meaning it uses pure GOD-like creative potential, meaning that it can actually create any effect it so chooses with it's power.
A cagey being though could ask Reim to make him immune to the magic of the Wuji, in which case Heart's Desire would counter Master of Magic.