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Mental Fortitude

Starting at 3rd level, whenever you are subjected to an Intelligence, Wisdom, or Charisma saving throw, you can choose to turn it into a Constitution saving throw instead. Once used, this ability cannot be used again until you take a short or long rest.

Return to Caster

Starting at 7th level, whenever you are hit with a melee or ranged spell attack from a levelled spell, you can use your reaction to absorb half of the damage into your weapon (so long as it is magical) that can be added to your next damage roll. This effect lasts until the end of your next turn. You can use this feature a number of times equal to your proficiency bonus per long rest.

Battle Attunement

Starting at 10th level, you can choose to attune to a magical weapon or piece of armor (including boots, helmets and gauntlets) with an action instead of the standard hour long process, however, you must make a Constitution saving throw when you do. (DC 14 for uncommon, DC 16 for rare, DC 18 for very rare, and DC 20 for legendary. This feature does not work for artifacts) If you fail the save, you gain 1 level of exhaustion and the attunement fails.

Warding Armor

Starting at 15th level, while you are attuned to a set of magical armor that is of rare or rarer quality, you can use your reaction in response to a spell being cast on or at you to give yourself resistance to its damage type until the start of your next turn, or to gain advantage on the saving throw it forces. 

Near Perfect Counter

Starting at 18th level, you gain the ability to cast counterspell at 8th level once per day.