Arcane Investiture

You endow yourself raw arcane energy and let yourself become a conduit for it. As you do, arcane force whirl around you. Until the spell ends, you gain the following benefits:

• You gain resistance to slashing, piercing and bludgeoning damage from non-magical weapons
• You gain 20 temporary hp. If the spell ends prematurely, any remaining temporary hp is lost. 
• You have advantage on attack rolls made with spell attacks
• Spell of 3rd or lower level that you cast automatically become third level spells
• You gain a fly speed of 60ft
• You regain a number of a total combined spell level of 5, none of which can be of higher level than third level.
• The DC of all your spells increase with 2 and you add 2 to any spell ability rolls (such as a counterspell roll).

Immediately after the spell ends, you must succeed on a DC 15 Constitution saving throw or suffer one level of exhaustion.

at higher level: when cast at a higher level, the spell grants 10 additional temporary hp for each additional spell level spend on it.