D&D 5E Mid- to high-level Wildshape [Moon Druids]

[Thurmas]

Perhaps you create a new breed of Giant Beasts. This is by no way scientific. Just spit balling.

Choose any beast that isn't already a giant beast or swarm. Double that creature's hit points. You increase it's CR, AC, saving throws and DC for any abilities it has by 2. Increase its size to the next size category. Double the number of damage dice you roll for any attacks.

The numbers may be off, but this just gives a run down of what I'm thinking.

 

[Weiley31]

Honestly, I wouldn't mind letting a Moon Druid upgrade their elemental forms to the Elemental Myrmidons. To balance it out, maybe add in two levels of Exhaustion once the transformation ends. And they can ONLY choose ONE Elemental Form to get upgraded.

That or you combine a beast form with one Elemental trait. Rock Giant Wolf Spider with Diamond coated webbing that can't catch on fire BUT acts like razor wire for enemies stuck in it?

An Air Dire Wolf that can knock people prone and then go through small openings to knock prone an unsuspecting guard in the next room. Nice!

A Water Pelican that can pour a stream of water from it's scooped beak to put a Forest fire out?

A flipping Flame Mammoth that shoots flames outta it's trunk like a Flamethrower?

Yeeeaaaah!

 

[Weiley31]

I feel like Monstrosities should be reserved for evil druids or Blighters of Tharizdun.

I feel like the Elemental Myrmidons would be an acceptable upgrade to the basic Elementals.

 

[FarBeyondC]

I just want to note, with regards to the intelligence limit of 5 placed on that item of yours, that beasts such as the Giant Owl and Giant Eagle have Int scores of 8, Giant Apes and Giant Elks an Int score of 7, and Giant Vultures and Dolphins an Int score of 6.

 

[Iry]

Elemental Myrmidons at 14 is definitely my solution.
I've dabbled with allowing Genies, but it basically came down to changing Moon Druids from /3 to /2 when determining the shapes they can use.