Angels possess a melee-range magic missile attack that they can use ignores both reflection and half spell damage, but deals no damage if you have magic resistance. The magic missiles they fire at range are similar to those from a wand of magic missile, but can be done at will. Like other monsters with magic missile attacks, angels have magic resistance.
Angels that are randomly generated almost exclusively appear in the service of one of the deities, and appear in large numbers on the Astral Plane; you can also obtain a guardian angel as a minion when you arrive on the Astral Plane if your alignment is sufficiently high and you are not causing conflict. If you are, however,
If you are lawful, randomly generated angels will be generated peaceful. In 3.6.0, 1⁄3 of randomly appearing angels will be minions of a random god from your pantheon; usually they will be peaceful to co-aligned players, but some will be made "renegade", and peaceful to cross-aligned players instead.
Angels are generated with a noncursed erodeproof large shield, with a 1/4 chance of the shield becoming a shield of reflection, and a blessed erodeproof long sword, with a 1/20 chance of the sword becoming either Demonbane or Sunsword if each artifact has yet to be generated, The tame guardian angel you get when entering the Astral Plane gets slightly better gear: their weapon is blessed and its enchantment raised by 1-4 points (if it's under +4), and they will be given an amulet of reflection if they do not get a shield of reflection.
The wand of death is completely ineffective against angels, and they have a good chance of having a shield of reflection, which neuters other attack wands and spells. They are cold resistant, but still vulnerable to fire, so casting the spell of fireball at Skilled or Expert might do significant damage; however, you may have trouble mustering the necessary power to cast spells repeatedly in most situations involving angels, which will usually occur on the Astral Plane while you are carrying the Amulet of Yendor.
When fighting angels in melee, Firebrand and Stormbringer are among the best weapon choices; however, on the Astral Plane, you will likely be seeking to find your high altar, so a footrice corpse will be preferable in that scenario, as is a wand of teleportation.
To avoid generating a group of hostile angels when you arrive on the Astral Plane, wait a few turns after you arrive before generating conflict.
He answered and said unto them, he that soweth the good seed
is the Son of man; the field is the world, and the good seed
are the children of the kingdom; but the weeds are the
children of the wicked one; the enemy that sowed them is the
devil; the harvest is the end of the world; and the reapers
are the angels. As therefore the weeds are gathered and
burned in the fire; so shall it be in the end of this world.
[...] So shall it be at the end of the world; the angels
shall come forth, and sever the wicked from among the just,
and shall cast them into the furnace of fire; there shall be
wailing and gnashing of teeth.
[ The Gospel According to Matthew, 13:37-42, 49-50 ]