Arcane Aegis

Your reflexes have been honed by the arcane energy suffused within your nervous system. You can instinctively release this energy as an Arcane Aegis when you or an ally are faced with the threat of attack as a reaction. The AC of the creature targeted by the spell increases by the caster's spell-casting modifier+1d4 and they may roll an additional 1d4 on ability checks and saving throws made before the end of their next turn, and add it to the total. The spell ends at the end of the affected creature's next turn. When upcasting the number of d4 rolled for each part of the spell increases with the spell slot level: 2d4 at spell slot level 4 or 5, 3d4 at spell slot level 6 or 7 and 4d4 at spell slot level 8 or 9.