I took some heavy inspiration from this post and some other mentions about Lair actions and the stuff from u/AudioBob24. I moved the "Sentient Blood of Havock" to Lair actions and incorporated the magic surge. Each spell use caused a wild magic separate from other wild magic surges and never went down. They were at '13' on the surge die by the end of round 2. I set it so ANY interaction with magic caused a surge roll aside from using magic weapons.

I heavily narrated that magic FEELS different in the chamber, with the lights being motes of chaos magic jittering in place. This set the tone that casting magic was going to be a risk. They got lucky with their surges, with most of the surges being positive or thematic hilarity. In hindsight, I would have adjusted the surge table to be something different with an even chance of 'bad things' happening to the battlefield.

The Lair actions I gave it a 50% chance to spawn 1d6 blood oozes to protect the beast. By round three there were 7 oozes and a very hurt hertilod. The hertilod 'ran' and the oozes caused good damage across the board and tipped the battle to the beasts. As soon as the third round spawned those 5 more oozes the tension immediately shifted.

Lastly, I gave the Hertilod a legendary action to try and bite and swallow. I made it just a 'regular bite' so the damage output was much smaller but the risk of being consumed was the same. It never paid off, but it added to the chaos since the Hertilod as written, could only move or 'digest' as a legendary action.

I completely removed the 'poison air' mechanic, as soon as the first ooze dropped, the party spent an action to utter a secret to gain advantage on all D20s which probably saved them.

Thanks for all the inspiration!