Trait

Razgruppa (annoying group in the Thiey're language)-  Thiey're fight as a single entity, their Spellcasting, Saves, and DC are always equal to 1/2 the number of Thiey're in an encounter. They only start an encounter if there is at least 20 Thiey're in the group. To cast a spell there must be enough thiey're to equal the spell level, each additional thiey're will add to the casting level. ie 4th level spell, minimum 4 thiey're to cast it 10 thiey're cast the spell as a level 10.

Spellcasting.

Each thiey're in an encounter has one of each of these spell prepared. And can cast it once without the need for any COMPONENTS, they count as psionic, and use thier minds to cast all spells. as such during an enounter they remain perfectly still to concentrate on their spells. 

The thiey're have following spells prepared:

Cantrips (at will): Poison Spray, Minor Illusion, Gust, Chill Touch, Vicious Mockery
2nd level Detect Thoughts
2nd level Blindness/Deafness
3rd level Bestow Curse
3rd level Tongues
4th level Confusion
4th level Phantasmal Killer
5th level Dream
8th level Antimagic Field
8th level Feeblemind
8th level Mind Blank
9th level Weird

Actions. Thiey're have no actions besides spell casting.

Thiey're have no physical abilities, and hide inside walls and other intimate objects, as such they are only discernible with a perception check (DC equal to the number of thiey're or a natural twenty), fairy fire will highlight them, but not the objects they are hiding in.

Reactions
Death Curse

upon death they cause psychic damage to the creature that killed them, causing 1d6 points of psychic damage.

Legendary Action: 

If there are more than 20 thier're in an encounter, once per encounter the group can cast:

Rasplenny o'kazobsluz: (minimum thiey're 20)while channeling this spell, the only actions their opponents can take are to retreat, or sleep. Any attempt at any-other action will be interrupted after they indicate what they are going to do, if the action was a hostile action they take full damage of the action as if it was a critical. Save DC is Wisdom equal to the number of Thiey're in the casting. If saved, prior to any action, the opponent will be informed of what is happening, and can inform the rest of their party for free. all other communications and chatter are silenced.