D&D 5E Need Encounter Suggestions for Archdruid's Animal Shapes

[DurrandDurr]

I have an encounter planned where an Archdruid that is devoted to an Aboleth (in a cracked Stone of Golorr scenario: it can communicate and Enslave only). The aboleth has enslaved a small town and their building an artificial lake to create its new home before being released from the stone. With a town full of enslaved/willing creatures, the Archdruid has nearly a 75 commoners she can turn into Large and Med. beasts (<CR4) via Animal Shapes with one concentration spell. (It's broken.)

When the enslaved townsfolk spot the (four, level 13) PCs coming to stop the final release of the aboleth, they telepathically warn the aboleth, and the Archdruid--15min away by the lake--changes a number of them into beasts to attack and defend. The unchanged humans at the lake will act as angry mob: being difficult terrain and create the grappled condition.

This creates an unusual, and fun, scenario of beasts working together that normally wouldn't. Any suggestions on how many beasts and what types to send after them without reaching overkill?
First wave: A squadron of Giant Eagles (x4) ridden by Apes (x4). I think more than 2 waves would become tedious. At the lake they'll have to fight the aboleth, archdruid, and an awakened tree. Should I keep some beasts there too?

Sure the PCs can one-shot an entire wave with a fireball, but once the beasts start turning into townsfolk when they reach 0 HP, they may need to change tactics.

 

[Quickleaf]

The lakeshore would be a fun place for a giant snapping turtle and some giant lightning eels. Maybe some giant toads who can swallow PCs to separate them, drag them underwater, or bring them before the archdruid or even unaffected peasants who are trying to break their friends & family free from the enchantment.

 

[tommybahama]

Have wave one be the villagers. They are covered in blood and rolling on the ground while wailing and gnashing their teeth when the party first spots them. When the villagers see the party, they will come running up to them with shock and horror on their faces. They will then mob the party and grab at them, trying to pull them apart. For every failed grapple check the party member is moved 10 feet away from the others. If they attack the mob then the it goes into a frenzy and gets advantage on its grapples. The mob can't be destroyed. It's just there for shock and horror.

Wave two should be aberrations instead of beasts using the Animal Shapes spell as you mentioned. Enough for a medium encounter. The mob still acts as difficult terrain for the party but not the aberrations.

Wave three should be a corpse flower. It slithers towards the party during wave two, spitting out a few Strahd zombies along the way. Give it a better move speed and extra HP for a medium encounter. Throw in a few saving throws against fear due to being attacked while being mobbed.

Once they kill the corpse flower the mob should fall to the ground exhausted by their efforts except for one old crone that turns to the party and says, "Ha, ha, ha. You have fulfilled the prophecy! Our dark god is awakened!!!"

Then bring on the Archdruid and Aboleth for wave four. The Awakened Tree is optional depending on the party's condition.