Arcane Weapons. The swordmage's weapon attacks are magical, and it uses its Intelligence modifier, instead of Strength or Dexterity, for the attack and damage rolls. When the swordmage hits with a melee attack using a weapon, the weapon deals an extra 3d8 lightning damage (included in the attack).

Spellcasting. The swordmage is a 10th-level spellcaster. Its spellcasting ability is Intelligence (spell save DC 17, +9 to hit with spell attacks). It has the following wizard spells prepared.

Cantrips (at-will): blade ward, conjure arms (new), fire bolt, shocking grasp, sword burst
1st level (4 slots): absorb elements, expeditious retreat, shield
2nd level (3 slots): cannon blast (new), misty step, shield other (new)
3nd level (3 slots): counterspell, lightning bolt, mass shield (new)
4th level (3 slots): dimension door, enhance body (new), march of blades (new)
5th level (2 slots): blazing thunderbolt strike (new), far step, steel wind strike

Weapon Bond. The swordmage has one or two bonded weapons. It can't be disarmed of those weapons unless it is incapacitated. If a bonded weapon is on the same plane of existence, it can summon that weapon as a bonus action on its turn, causing the weapon to teleport instantly to its hand.

Multiattack. The swordmage can cast a cantrip. It then makes two longsword attacks.

Longsword. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 9 (1d8 + 5) slashing damage, or 10 (1d10 + 5) slashing damage if used with two hands, plus 13 (3d8) lightning damage.