So I am working on an encounter for my party. it is the final confrontation with one of my players arch nemesis from their back story. He is a half orc named Skorm and is basically a gangster/bandit king type character.

They are assaulting his strong hold and I have it pretty well populated with Skorm, his soldiers, cannon fodder and traps, but I want to add one more layer of challenge in some kind of guard creatures that can be wandering around or stationed in specific places.

the party is made up of a bard/rogue, cleric/sorceror, fighter, barbarian/fighter, artificer, and druid rogue all level seven and a ranger/rogue at level 8, so pretty well balanced in combat and support. This is supposed to be a HARD encounter for them, the hardest they have faced yet, not purposefully trying to kill anyone but a real and significant chance of it happening.

I can throw in some wolves or guard dogs, but I am looking for something more fun with some flavor for this finale of the story for the character. So what are your suggestions for realistic guard type creatures for a bandit king type character who has carved out his own little slice of the country side, has a small army of ~100 soldiers, in his stronghold?

Have you considered the (often neglected) Otyugh ? They prefer being subterranean but will work with humanoids if they are consistently well fed. 

If you want something cool, a Chimera or a Manticore (they won't be together) would make for a nice surprise.  They will happily work with a humanoid as long as they are compensated.  Unfortunately, Skorm is unlikely to have more than one of them but could make for a surprise treasured 'pet' guarding him personally.

Have you already included Ettins in your cannon fodder - they will often work with Orcs, but, obviously, less of a guard dog type.

I know this is dnd so there is magic (duh) but what type of magic is available, or how willing are you to use it. If this bandit king is as rich and powerful as you say, he probably can hire powerful allies. Devils and yugoloths are powerful creatures that enter in to contracts with people. People can also hire others to summon elementals, demons, or a whole lot of other extraplanar beings.

If those don’t really fit the vibe of the campaign look for other good monsters that could be bribed. bestial creatures given sentience are also quite good. Kruthiks are some of my favorite and can be deadly in packs.

my 2 suggestions regardless of what you choose, are some combination :

1: lower power enemies (like Kruthiks or similar) that alert other members who will gang up on them.

2: more powerful enemies (Cr 9 or higher) that pose a threat by themselves. Give them legendary actions so the players don’t overrun them in a round, and give them at least 1 legendary resistance so hold person or another spell doesn’t make them go down early.

Quote from Holton_Coalfield >>

Have you considered the (often neglected) Otyugh ? They prefer being subterranean but will work with humanoids if they are consistently well fed. 

If you want something cool, a Chimera or a Manticore (they won't be together) would make for a nice surprise.  They will happily work with a humanoid as long as they are compensated.  Unfortunately, Skorm is unlikely to have more than one of them but could make for a surprise treasured 'pet' guarding him personally.

Have you already included Ettins in your cannon fodder - they will often work with Orcs, but, obviously, less of a guard dog type.

 Those are great suggestions, I hadn’t considered the Otyugh, but Skorms stronghold IS built in to the side of a mountain so that would work quite well! 

I hadn’t considered including Ettins, but they could work quite well swapped out for a couple of the groups of bandits roaming the halls!

Quote from Bybyroro >>

I know this is dnd so there is magic (duh) but what type of magic is available, or how willing are you to use it. If this bandit king is as rich and powerful as you say, he probably can hire powerful allies. Devils and yugoloths are powerful creatures that enter in to contracts with people. People can also hire others to summon elementals, demons, or a whole lot of other extraplanar beings.

If those don’t really fit the vibe of the campaign look for other good monsters that could be bribed. bestial creatures given sentience are also quite good. Kruthiks are some of my favorite and can be deadly in packs.

my 2 suggestions regardless of what you choose, are some combination :

1: lower power enemies (like Kruthiks or similar) that alert other members who will gang up on them.

2: more powerful enemies (Cr 9 or higher) that pose a threat by themselves. Give them legendary actions so the players don’t overrun them in a round, and give them at least 1 legendary resistance so hold person or another spell doesn’t make them go down early.

 Skorm has a few wizards in his employ he keeps nearby, he keeps a conjuration and a necromantic wizard in his inner chamber along with his elite guard as his last line of defense. 

I considered having a couple of demons, but they just got done with a whole demon thing, and one of the other players has a separate situation with a demon that will take pretty likely have them wind up in avernus, if not deeper in to the nine hells they  are going to have to deal with at some point, so was avoiding over using demons. 

Kruthiks are an interesting idea, I had some goblin and kobold swarms for them to deal with, the party is balanced well for combat against small groups or one on one enemies but don’t have a lot of AoE strength so swarms can give them trouble, but a few of those running around in packs might be a less tedious challenge than a whole swarm of lower level minions. 

Well it might be a kinda difficult battle, but maybe the Jabberwock from wild beyond the witchlight? It’s CR 13 but it has low hitpoints and its regeneration is countered by slashing damage. It’s deadliest ability is whats basically a 30 foot confusion aura, but I think it wouldn’t be too difficult for a party of level 8s.

Guard Drakes are made for this. Expensive gifts from dragons that grow up to be fierce watchdogs for whoever they imprint on after hatching. Plus then there may be some eggs or newly hatched Drakes for potential RP/story stuff. 

Their CR is low compared to our party level, but you could maybe place a trap that lets out a poison gas cloud like the Stinking cloud spell and then releases animated armors. They don't breathe and have blindsight so they can make the most out of it.

guard geese. they can tell a stranger from a regular member on sight and their alert draws the attention of humanoid guards. and that's ignoring that on their own they can knock someone prone, potentially break bones, and generally be more aggressive than dogs. or at least that's how they are in real life (might be nerfed in game).

if there's room for a pond in the keep, then sink an unnoticed magic item down there that gives the geese a (single) magical power the bandits might not even be aware of... iron skin, misty step, breath weapon, enlarges when attacked, echo knight double, glowing red eyes: see invisible + heat metal, magical fear honk, magical confusion honk, etc.

I should think Skorm, or any egotistical baddie, would love the idea of having the party turn on itself as a prelude to the final encounter. There are spells, items, and creatures that could have the party become their own worst enemies. You'd just need to ensure enough of them fail any save so they WOULD fight each other. Even just a few rounds of combat this way can soften them up for Skorm to feel confident in taking them out.

Then the weakened party would need to fight smarter to win the day...

Thank you all for the great suggestions, these should be an epic encounter!

gaurds, gaurds, gaurds. orcs, orcs, orcs. consider the CR 8 grey render. its bonded to skorm and gets telepoted and healed by the magikoopas. you really only need one that can be everywhere at once