Arcane Guardian

Arcane Strikes. When the arcane guardian hits a creature with a weapon attack, it can expend one ranger spell slot to deal damage to the target, in addition to the weapon's damage. The extra damage is 2d8 for a 1st-level spell slot, plus 1d8 for each spell level higher than 1st, to a maximum of 5d8. The damage can be acid, cold, electricity, or fire, chosen each time you activate this power.
Arcane Familiarity. The arcane guardian has advantage on any saving throws to avoid being charmed or frightened.
Spellcasting. The arcane guardian is an 11th-level spellcaster. Its spellcasting ability is Wisdom (spell save DC 12, +4 to hit with spell attacks). The arcane guardian has the following spells prepared:;
1st level (4 slots): Compelled duel, Hunter's mark, Searing smite
2nd level (3 slots): Magic weapon (already cast before the encounter), Mirror image
3rd level (3 slots): Counterspell, Protection from energy

Multiattack. The arcane guardian can make three Longsword attacks.
Longsword. Melee weapon attack: +6 to hit, reach 5ft., one target. Hit: 7 (1d8+3) slashing damage, or 8 (1d10+3) if used two-handed.
Heavy Crossbow. Ranged weapon attack: +5 to hit, range 100/400ft., one target. Hit: 7 (1d10+2) piercing damage.