Cadius Thane

 Steel Mind. Cadius has advantage on saving throws against spells and other magical effects.

Magic-Infused Weapons. Cadius’s weapon attacks are magical.

Spellcasting. Cadius is a 12th-level spellcaster. His spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). Cadius can cast absorb elements and longstrider at will and has the following artificer and wizard spells prepared:

Cantrips (at will): booming blade, mending, shocking grasp, thorn whip

1st level (4 slots): burning hands, catapult,  grease

2nd level (3 slots): misty step, scorching ray, heat metal

3rd level (3 slots): counterspell, haste, lightning bolt

Multiattack. Cadius attacks twice with his Electric Armblade. He can forgo one of these attacks to make a ranged Fire Cannon attack. He can also use one cantrip in place of one of these attacks.

Electric Armblade. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 15 (3d6 + 4) slashing damage. The target must make a DC 14 Constitution saving throw, taking 21 (6d6) electric damage on a failed save, or half as much damage on a successful one. 

Fire Cannon. Ranged Weapon Attack: +7 to hit, range 60/150 ft., one target. Hit: 7 (1d8 + 3) piercing damage plus 13 (3d8) fire damage.

Protective Plating. As a bonus action, Cadius can gain temporary hit points equal to his CR, replacing any temporary hit points he already has. He can use this bonus action a number of times equal to his proficiency bonus (4 uses/day), and he regains all expended uses on a new day.

Improved Prosthetics. Cadius can take the Dash action as a bonus action.

Absorbtion Core. Cadius can cast absorb elements as a reaction.

Cadius Thane can take 2 legendary actions, choosing from the options below. Only one legendary action can be used at a time and only at the end of another creature's turn. Cadius regains spent legendary actions at the start of his turn.

Attack. Cadius makes one Electric Armblade or Fire Cannon attack.
Dash. Cadius takes the Dash action.