Solar

A solar arriving on the party's side is the finale of someone's storyline, not a tactical pickup. Solars are sent by gods. They show up because a deity has decided the party's current problem requires direct angelic intervention, and they will return the moment the assignment is complete. Treat the visit as a single-scene event with a clear arrival, a clear purpose, and a clean exit.

Lead with what the solar can do that no PC can. Slaying Bow auto-kills any creature it hits with 100 HP or fewer on a failed DC 21 Dex save. Use it once, on the named lieutenant the party has been failing to catch for four sessions, and let the players watch the bolt of light remove the problem in one action. Resurrection (1/Day) brings a single dead PC back without the costly material component. Commune lets the solar ask a god three yes-or-no questions on the party's behalf, which is your chance to telegraph the next arc cleanly. Control Weather changes a siege.

In actual combat, the solar opens with Multiattack: two Flying Sword attacks at +15, reach 10 ft. or range 120 ft. (the sword returns each turn), 22 slashing plus 36 radiant per hit. Replace one of those with Slaying Bow against the worst creature on the board. Divine Aid as a Bonus Action up to 3/Day casts Cure Wounds (level 2), Lesser Restoration, or Remove Curse on a downed PC. Spend legendary actions every round on Blinding Gaze (DC 25 Con or Blinded for 1 minute) and Radiant Teleport, which is your reposition plus a 10-foot DC 25 Dex burst at the destination.

The solar leaves. Once the assignment is fulfilled, it speaks one sentence to whoever the deity wished it to speak to, and ascends. Do not let it linger. Do not let the party ask follow-up questions. The grace was given, the grace is gone.

Write the solar's arrival line and its departure line before the session. Improvising either of them will undercut the entire scene.

A solar fighting against the party is the campaign-ending version of the tragic-misunderstanding setup. A god has been deceived. A relic the party recovered is sacred to the wrong celestial order. A PC's patron has finally been judged and the verdict came back guilty. Sell the setup for a full session before swords come out, because a solar that is wrong about the party is a story, and a solar that is right about them is the credits.

Once the fight starts, the solar opens with Slaying Bow at 600 ft. range, DC 21 Dex save, and any PC with 100 HP or fewer dies on a failed save. That is a real threat for almost any party of medium tier. After the bow, two Flying Sword attacks at +15 averaging 58 damage each. Hover at 150 ft. of fly and pick the angle. The solar has Truesight 120 ft., 24 Passive Perception, and Magic Resistance with advantage on saves against spells, plus 4/day Legendary Resistance. Casters cannot lock it down. They can only outlast it.

Spend legendary actions every round. Blinding Gaze at DC 25 Con shuts down the rogue, the fighter, the archer, anyone who needs to see to act. Radiant Teleport is your reposition plus 11 radiant in a 10-foot emanation at the destination. Pair them: teleport into the back line, force the Dex save, then Multiattack the cleric next turn.

If the solar dies, it reforms in Mount Celestia at full HP via Exalted Restoration. The party has not killed it. They have postponed it. Make sure the players understand that before the final blow, because the choice to push past Slaying Bow becomes a different decision once they know the angel is coming back.

Have the solar tell the party exactly why, in plain Common, before the first save is rolled. The tragedy needs words.