what is the meaning of '[U]' in spoilers file

[rader.wang]

Just now , I was killed by "Bullroarer the Hobbit (Light Umber 'h')"
and i find this monster's info in spoilers file...
before the name of this monster, there are 3 characters '[U]' .

[U] Bullroarer the Hobbit (Light Umber 'h')
=== Num:76 Lev:5 Rar:3 Spd:+10 Hp:60 Ac:12 Exp:90
He is a sturdy hobbit who is renowned for his unusual strength and vigour.
He can prove a troublesome opponent.
This creature is normally found at depths of 250 feet (level 5), and moves
quickly. He may carry up to 3 good objects. He can open doors and bash
down doors. He resists bright light and rock remover, and does not resist
acid, lightning, fire, cold, poison, water, nether, plasma, nexus, or
disenchantment. He takes quite a while to see intruders, which He may
notice from 160 feet. He can hit to attack with damage 1d8, and hit to
attack with damage 1d8.

what is the meaning of '[U]'?
It means boss?hard to kill ,dangerous?

[Mondkalb]

That probably stands for "unique".

There are roughly 100 unique monsters in Angband, which are usually a bit tougher than other monsters of their class.

[rader.wang]

That probably stands for "unique".

There are roughly 100 unique monsters in Angband, which are usually a bit tougher than other monsters of their class.

I see, thank you


He can hit to attack with damage 1d8, and hit to
attack with damage 1d8.

means

in one turn, he may attack me with damage 2-16

?

[Mondkalb]

Sound plausible.

[Pete Mack]

Yes, but with two separate rolls the variance is much lower than with a single roll. Also, most creatures have more than one type of attack, so the 2d6 really doesn't help for them.

[Pete Mack]

Just now , I was killed by "Bullroarer the Hobbit

What class are you playing?
The only class really vulnerable to Bullroarer is Priest, although with !Hero and Blessing, he has a pretty good chance.
Mage should detect him and run away.

Other classes can kill him pretty easily with ?Phase door, !Oil and !Hero.
If you aren't carrying these (along with CLW, CSW and/or CCW), you should be...

Also: read the Player's Guide. (It mentions Bullroarer by name!) You don't need to take all the advice about diving, but some of it is really important.

[Derakon]

Bullroarer is dangerous, as a fast enemy with decently strong melee. If you're a newbie, then you won't know how to be prepared, and thus he's liable to chalk up a kill on you. Fortunately, as you said, there are ways to deal with him -- the main lesson here is "have a ranged attack", since that plus even one Phase Door will take away much of his health; he's not very durable at all.

[Pete Mack]

Bullroarer is dangerous, as a fast enemy with decently strong melee. The main lesson here is "have a ranged attack", since that plus even one Phase Door will take away much of his health; he's not very durable at all.

There are two "main lessons". One is use ranged attack for heavy hitters. The other is: monsters are only dangerous if you let them attack(!)