Erelim

 Erelim medium, celestial (any good alignment)

AC 18 (natural armor)

HP 127 (15d8+60)

STR    18/+4

DEX    14/+2

CON   18/+4

INT    11/+0

WIS   12/+1

CHA  14/+2

Skills: Perception +4, Insight +4

Resistances: necrotic, radiant; bludgeoning, piercing, and slashing from nonmagical attacks

Immunities: poison

Martial Fury. As a bonus action, the sword wraith can make one weapon attack, which deals an extra 9 (2d8) radiant damage on a hit. If it does so, attack rolls against it have advantage until the start of its next turn.

Actions

Longsword. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 8 (1d8 + 4) slashing damage, or 9 (1d10 + 4) slashing damage if used with two hands.

Longbow. Ranged Weapon Attack: +5 to hit, range 150/600 ft., one target. Hit: 6 (1d8 + 2) piercing damage.

Call to Honor (1/Day). To use this action, the Erelim must have taken damage during the current combat. If the sword wraith can use this action, it gives itself advantage on attack rolls until the end of its next turn, and 1d4 + 1 spectral warriors (LG sword wraiths) appear in unoccupied spaces within 30 feet of it. The warriors last until they drop to 0 hit points, and they take their turns immediately after the commander's turn on the same initiative count.

Find Steed (at will). 2nd level spell. The Erelim summons a spirit that assumes the form of an unusually intelligent, strong, and loyal steed, creating a long-lasting bond with it. Appearing in an unoccupied space within 30 feet, a celestial warhorse appears. The Erelim  can't have more than one steed bonded by this spell at a time. As an action, it can release the steed from its bond at any time, causing it to disappear.