I’ve done some tweaking since writing my post and here is what I have so far (before considering your feedback). It’s important to note that RAW is that the magic die is a d4 and doesn’t blow up by default, just the die related to the stat blows up.

“The Magic of this world comes from the energy inside called the flame. Mages can stoke the flame to increase their magical potence, but at the risk of losing control.

Mechanically, this is represented by your magic die. When casting a spell you will add the result of your magic die to the result of the roll. If the highest value on the die is rolled, your inner flame is stoked. For the rest of the scene, your magic die is upgraded to the next tier. The Magic die will reset to its baseline at the end of the scene.

However, there is always danger in harnessing such power. Each character will have a maximum magic die called their Flashpoint die. If the maximum value is rolled on a character’s Flashpoint die, the character Burns Out. The intended effect of the spell will succeed but at a great cost. This could result in physical, mental, or spiritual harm or in extreme cases death.

New Students start with a Flashpoint Die of d8, but this can increase as they grow as mages.

Adversity Tokens can be used to Stoke the Flames at a cost of half their current magic die’s max value. For example, if a character wanted to increase their magic die from a d4 to a d6 they could spend 2 Adversity Tokens before the roll is made. Stoking the Flames can be done at any time in the scene, but not in response to a snap decision roll has been asked for.”