Variety of summonings for my BBEG

[King of Nowhere]

My main BBEG for the campaign is a crazy nymph who accidentally gained control over a wild magic zone, and, long story short, in her madness decided to destroy the world.
She's a druid with a few monk levels, she's got crazy defence with sky-high saving throws and AC and some unique elusive abilities, she packs a good punch in offensive spells, but her main features are creatures. Mutated creatures.
Commanding the wild magic, she also controls the mutated creatures living in the area, and can breed them and use them for conquest - meaning they will be encountered well before the party is ready to personally face her. She also has a unique perk of a summon natural ally IX for free every round in addition to any other spell she may cast, and she never runs out of spells as long as she's in her home turf - the wild magic is empowering her spellcasting. And every creature she breeds or summons is mutated in some way.
I have found and statted the most common summons she'd use, here I am looking for help finding more stuff that she could summon

what I have so far:
- mutations: every time she summons a creature, roll a d6 and apply
1) the creature has a tentacle; it gains an additional slam attack. Alternatively, the tentacle ends with a mouth, so it gains a bite attack
2) the creature is covered in armored tumors, gaining a bonus to AC and CON
3) the creature has a breath weapon, either on its regular mouth or it has an additional mouth where it shouldn't have
4) the creature has all its legs swapped with arms. It cannot move, except maybe by crawling, but it gainsas many slam or claw attacks as it had legs
5) the creature is a conjoined twins; it has a second bite attack, and for most effects that affect a single target it can roll twice the saving throw
6) the creature is half plant, gaining the greenbound template

I empowered her summonings with augment summonings, ashbound, child of winter, and rashemi elemental summoning.
Rashemi elemental summoning gives her elemental the orglash template, which adds some minor boosts and - most important - gives them a cone of cold spell-like ability. She generally uses that for offensive potential, especially because even at high level most foes would take some damage from that. the template can be applied to air and earth elemental, but for obvious reasons it doesn't make much sense applied to fire and water elementals.
Child of winter give her access to colossal scorpions, her favored heavy combat summoning. With augment summoning and ashbound, they top at +39 to hit, enabling them to damage even the most armored targets. If she cannot overcome a target with her magic, and it's immune to the elemental's cone of cold, the BBEG starts summoning three of those per round until the target is overwhelmed.
child of winter also gives her access to hellwasp swarms, but she already has a lot of those (she breeds them), that she uses to take control of other npcs. anyway, they were her trump card to take a city defended by heavy weaponry, but in a normal high level combat they aren't very useful.

So far, then, the BBEG is going to rely mostly on colossal scorpions and air/earth elementals. Occasional sprinkle of hellwasps, but I expect the party to discover weapon crystals to damage swarms, and with those they will lose their main appeal (namely, that the party has to waste spells to deal with them)
This nymph and her forces will be the major opponent for the rest of the campaign; for the sake of variety, I would like to have encounters with creatures other than colossal scorpions and orglash elementals.

For the sake of making those encounters meaningful, those creatures should be capable of hitting AC 40 at least a few times. I run a high magic world, and high loot translates to high AC, which makes most summoned monsters useless.

Thanks

[SpicyBoi_Nezu]

Something that I would look for, as someone who enjoys breaking the game, is spells other than summoning. Not necessarily buff spells, but area spells paired with metamagic to lay down some variety to the battlefield. A very basic one that can climb it's way to high levels with the right metamagic is Kelgore's Gave Mist, offers no save against the cold damage, but by pairing it with metamagic that allows it to apply different effects when it affects a character, it adds some spice.

Looking at Planar Ally/Binding is a good next option, it allows you to "summon" some generals/underlings that are far more intelligent and have many more uses, and the best part is, when they die, they return to their plane and can be summoned again. This really only works if your really high level, players can't even begin to abuse this until at least 15th-17th level, and seeing how high you're going, this can offer some very diverse options.

Another option is to overwhelm them with numbers. In 3.5, a level 20 fighter cannot win against 800 goblins. The max he can kill each round is around 20, and the goblins can statistically do around 10 damage per round, with 5 goblins per round rolling a 20 and dealing 2 damage. Swarms are nice, but if you clutter the battlefield with enough summons, each with 20 hp, your spellcaster better hope they have enough AOE spells, and the melee better hope they have Great cleave. Depending on how high level of spellcasting this character is, you can get quite a lot of creatures out in one round. I had a necromancer that could create 650HD of undead per round for 108 consecutive rounds, given enough corpses. If the battlemap has an enemy in each square, each with attacks of opportunity, statistically speaking, that's a nightmare.

The final, and most broken option, is Epic Level custom spell creation. My DM has used this a few times, each time, our party was under level 12, and I can't imagine the limits if applied to a level 20 party. My favorite was a custom spell called Apocalypse, where the BBEG spent 24 hours casting a spell that encompassed an entire continent, and turned it all into a desolate wasteland. The sky isn't even a limit once you really get into it, at 40th level, space travel becomes easy. This requires an immense amount to research and effort, but all the mechanics are there.

Finally, may I reccomend a single CR24 enemy that is a tad stronger than the CR reflects, you can't summon it, but crafting it is possible. The Elemental Colossi trio. Despite their name, they are colossal golems, and they have a fun quirk to them. They are immune to magic, and have a permanent Anti-Magic Field with a 100 ft radius around them. 40 AC, 432 hp, +70 to hit, construct traits, and 30ft reach. That's just he CR24 Stone version, the CR33 Iron version has 60 AC, 608 hp, +99 to hit, construct traits, magic and rust immunity, and a 80ft cone DC 58 fort save poison breath attack that does 3d6 temp con damage initial and 2d6 temp con damage secondary. When they no longer have their magic items, spells, or spell like abilities functioning, those stats seem a little bit scarier. This is best kept as a secret weapon, since the antimagic affects you as well, but is scary nonetheless.