They are a magical embodiment of an aspect of life. Some creatures can easily embody much of these aspects an draw out the power of it to help, harm, or hinder any obstacles in their way. Many of the tales surrounding these people and their strange inherent ability gave rise to the moniker, "Fate Crest," and soon enough belief anyone marked with these amazing magical sigils would be capable of defying The Fates themselves. The attainment of these marks are cryptic in of themselves. For some marks, they must be earned by trials or rites of ancient civilizations. Some can simply appear in dire circumstances, or in circumstances where a person is chosen for already embodying much of the idealism behind the mark. Power from these sigils differ from studied magics, deriving from a different source than divine magics - making any who carry these marks an intrinsic subject for planar and extraplanar people. Angels & devils alike may try to persuade, or even covet, the magic of these crests. Wizards & mages might try to utilize such an important person for political or magical gain.
The true folly of those that carry this mark is the inherent hubris, for as unchecked power grows it can become far more difficult to stay grounded in what the person once believed.
There are 3 levels, 3 categories. The uses of spells increases by 1 per level. For applications..
- offensive is the first category.
- Level 1 you can command a creature to strike for your bonus action.
- Level 2 temporarily gives the creature powers of a wielded weapon when a spell is cast. That creature may only benefit from one weapon at a time.
- Level 3 able to dominate and command multiple creatures at once.
- Defensive is the second category.
- Level 1 provides temp HP equal to your proficiency bonus when you cast a spell
- Level 2 provides a bonus to the animal's saving throws.
- Level 3 mayhaps mounted combatant but for spells
- Utility is the third category.
- Level 1 allows conversation with additional type of creature fluently
- Level 2 able to summon friendly creatures to your side equal to your proficiency bonus. Must be creatures you can speak to.
- Level 3 mayhaps Druidic wildshape
Even if you go down one path - based off how you manipulate or find yourself using the mark, you will gain (based on DM) one of the boons at appropriate levels. Depending how you use your mark or play it up, you could get 1st level utility, 2nd level offensive, third level offensive. The important bit is that you get boons based off how you first start envisioning or using the mark.