Polymorph in its current form may be a bit too much, specifically for managing powerful enemies. This is the kind of spell that forced Lengedary Resistance to exist; a save or die that is so powerful and cheap that if something fails it, the encounter can be over before it begins.
On the problem of polymorph, by Carl Olson
D&D 5E - Polymorph Shenanigans EN World Tabletop RPG News & Reviews
True Polymorph 5e D&D Guide
D&D 5E - Polymorph question (She turned me into a NEWT!!!I got better.)
10 Best Things To Polymorph Into (D&D 5E) – FandomSpot
OC] For the book lovers: The Book Wurm – a highly venomous critter, stats included : r/DnD
Dealing with Polymorph? : r/DMAcademy
That's a lot of polymorph : r/dndmemes
On the problem of polymorph, by Carl Olson
OC/AI] -upgraded- My DM let me polymorph a baddie into a newt if I made a stat block for it. He got better in about an hour : r/DungeonsAndDragons
What is True Polymorph 5e guide: THIS is HOW you use it! - Creature College
D&D 5E - Polymorph Shenanigans EN World Tabletop RPG News & Reviews
On the problem of polymorph, by Carl Olson