XVARTS

using the sidekicks ua and xvart warlock together...

ok, so the queen of these xvarts is a xvart warlock named MAJAR the UNBLINKING as in Volo's Guide with few changes, she has boots of striding and springing, a rod of the pact keeper +1 and a shield +1
35hp, ac18 with a +1 shield

 but her champion is this guy...

STRITTEN BLAXT (XVART BATRIDER HEXCASTER)
hp 10d6+10 (70hp)
a xvart warlock with 5 levels of spellcaster (cleric)
that replaces its 'spellcasting' trait
but he still has innate spellcasting which is detect magic and mage armor at will, so we'll keep him in no armor. (AC15)

xvarts have the thing where they can communicate with rats and bats, and with giant bats and rats. so i would put this guy on a giant bat mount and have him oversee fighters on the ground...

(there are like 400 xvarts in this stack, not includign the ones outlined here.)

that gives him a range of 60ft. and the bat also makes its bite attack which adds another (+4/d6+2) damage. i would let him use the xvart disengage and shove proficiency for the bat. so advantage on shoves if theres an ally in 5ft of the target. then he uses his whole move to shove and disengage, making no attacks.

give him a shortbow, so its...
(+4/d6+2) either with the bow or the scimitar ... and flavor him a sort of branding iron thing instead of a scimitar, that does burning damage.

so ill give him... does a melee attack, which is also casting a touch spell with the branding iron, the bat makes a bite attack, and disengage in the same turn.

stealth +3
give him wisdom 16 (+3) and constitution 14 (+2)
wisdom based casting (+6/ DC14)
wisdom saving throw (+6)

[1][1][1][1][2][2][2][3][3]

three cleric cantrips (thaumaturgy, guidance, resistance)
1st level spells (bane, guiding bolt, cure wounds)
2nd level spells (lesser restoration, blindness/deafness)
3rd level spell (bestow curse)

so buffs and debuffs, some touch spells, some healing.

on a short rest, recovers 5 points of spell slots.

----------------
REXVOLT, JARN and YESRA, XVART BATRIDERs
so i'll give him some level 3 lieutenants. these guys can be based on regular xvarts rather than warlocks.. with 16 dex, so ac14(leather armor) and 30 hit points each. im giving them three levels of warrior.

proficiency (+2) in athletics, acrobatics, and animal handling

theyre also bat riders, basically to confuse which guy is the spellcaster. stritten goes into stealth, these guys pop out. so they also do the disengage and shove while on bats. im picturing a lot of narrow platforms over pits in this cave.

so shove is a str-athletics check opposed by the targets dex-acrobatics check. so these guys are the best at the shove thing, having advantage +2 if an ally is adjacent to the target. the shove knocks you prone or

they make an attack or a bat attack, not both, and theres generally no reason to use the bat's bite rather than shove or arrows.

 they make bow attacks and scimitar attacks at (+5/d6+3) and also make bat bite attacks at (+4/d6+2)
they also crit on a 19 and have advantage on dex saves they can see.

then some roguey ones on the ground...

-----------------
SALM, JISBIT, SILSBY and CLAX, XVART WHISPERERs - these ones are (level 2 expert) speakers, so they speak either common or goblin. call them 15 hp.

proficiency acrobatics, slight of hand, stealth, insight, survival, with expertise in insight and survival.

they do net attacks (+4, 10 feet) or mallet attacks (+4/d6+4)... but nonlethal. but can disengage, dash or hide as a bonus action. these guys automatically crit against a foe on the ground.

------------------
okay, so the theme with these guys is theyre noble avatar smurf types who are just trying to maintain their secret homeland, but the place is also a beholder lair or such (who they sort of believe is an avatar of their god, the NIGHT HUNTER) and the beholder guy is starting to pull planar terrors into the world....

so they will prefer to scare off adventurers rather than kill them, the idea is to rough them up, dump them out of the dungeon and make it so that they dont come back. I think if they tpk the party, they will take 1 eye and dump the party outside.

treasure.... majar would have a bunch of gold jewelry covered in moonstones, 2000 gold worth. a +1 rod of the pact keeper. a +1 shield. and a boots of striding and springing.