Blunderbore

These monstrosities deal Crushing Blows. This ability makes them extra useful for summon necromancers. With an army of Revives, summoners can complete Pandemonium Event.

All Blunderbore class monsters regenerate hit points 100% faster than usual (2x the rate), and the regeneration rate increases with the difficulty level.

Poison, Open Wounds, and Prevent Monster Heal stop hit point regeneration while active.

Blunderbore are the only family of monsters in the game to use Crushing Blow (CB), reducing health by a percentage. Coupled with their chance to Stun via Smite (slvl 1/4/8 in Normal/Nightmare/Hell = DMG+% 15/60/120 & Stun 0.6/1.2/2s), greatly increased health recovery (100%), and fairly high damage, defense, and hit points, these make them quite formidable foes and require extra precaution to face - especially in larger packs.

They have a Crushing Blow chance of 15% in Nightmare and 25% in Hell. Their chance of Smite is 60% in Normal and 65% in Nightmare and Hell. All the aforementioned attributes also make them a uniquely fantastic source for Revive to a Necromancer, especially for fighting Uber bosses at the Pandemoneum Event.


Regarding spawn chances, sorted by Act then probability (which happens to correspond to level progression per Act):

Act II:
1. Harem Level 2 | Blunderbore | 3/5 (60%)
2. Palace Cellar Level 1 | Blunderbore | 3/5 (60%)
3. Palace Cellar Level 2 | Blunderbore | 3/5 (60%)
4. Palace Cellar Level 3 | Blunderbore | 3/5 (60%)
5. Tal Rasha's Tomb | Gorebelly | 3/7 (43%)

Act III:
6. Durance of Hate Level 1 | Mauler | 3/4 (75%)
7. Durance of Hate Level 2 | Mauler | 3/4 (75%)

Act IV:
8. River of Flame | Urdar | 3/7 (43%)

Act V
9. Frigid Highlands | Blunderbore | 3/10 (30%)
10. Pit of Acheron | Mauler | 3/10 (30%)

Some fun fact Lore about the Blunderbore variants, from the tabletop Diablo II: To Hell & Back's monster summary:

Blunderbores were the prototype of all Blunderbores to come. Though less advanced, they are still a menace when taking orders from their evil lords.

Gorebellies eat any meat they can find, in any condition. Like most Blunderbores, they do not even put their food down to fight.

Maulers take thick-witted joy in pounding on things. If they have nothing to attack, they will punch buildings, the Ground, or each other.

Urdars are the newest and smartest of the line. Their power is great enough that the lords of hell keep them as bodyguards and as highly resistant torture subjects.

One oft-overlooked quality of the Blunderbore is its capacity to threaten Sorceresses relying on Energy Shield for their durability. The life reduction associated with Crushing Blow completely bypasses Energy Shield. This can leave a Sorceress low on life at a critical moment when the life orb would have otherwise remained untouched.

May appear as Act 5 Guests in:

Blunderbores (blunderbore5) can spawn in:
Frigid Highlands
Maulers (blunderbore6) can spawn in:
Pit of Acheron

https://diablo.fandom.com/wiki/Blunderbore_(Guest)

My favourite bound Demon so far for a Demon Warlock.

For the Blood Boil build the best combo I've tested and found to my greatest liking is:
1) a unique,
2) bound while Extra Fast is active in a TZ (boy, they bolt like a bat outta hell, these chaps),
3) with the Amplify Damage curse ( Conviction aura is nominally good, too, but I found it less efficient, seems like Physical damage from Blood Boil is generally much more effective on cursed monsters),
4) with the Holy Freeze aura.

Bound uniques are often immune to Physical damage, since they are Extra Fast they reach the mobs almost instantly even without the Death Mark. Holy Freeze keeps the mobs broken by Amplify Damage away from you while you Blood Boil them to smithereenes.

The only minor downside is some mobs literally shatter (because Holy Freeze) so you have a little less carrion for Engorge but it's pretty much negligible considering the benefits.