Archon, Stage 3 (Paradigm Shift)

You have advantage on saving throws against spells / magical effects and resistance against damage caused by spells specifically.

Flaw:

Unfettered. Being a creature of pure energy you are severely hindered in an area of Anti Magic and Silence. Each time you start your turn in such an area you take 1d10 Force damage that goes through resistances and immunities. Your maximum hit points also decreases by the same amount. When your maximum hit points are reduced by this effect, they return to normal after you finish a long rest.