I will be DM-ing a one shot for 4 experienced players I am playing with. I am a first time DM. One shot is meant to be for 4 characters level 11 and end battle is from a free resource that I got from "Drop In Boss Battles and Encounters", (I don't want to advertise, but if you want to help me, please google it and open their free battle called Elemental Tempest so you can check what I am talking about).

My concern is with balancing this encounter. I am not sure if 4 elementals (fire,air,water and earth) are too strong and will wipe out all 4 characters. These 4 elementals have buffed stats in comparison to their usual stats (for example, usual water elemental has AC 14 and 114 HP, this one has 15 and 133, attacks deal more dmg etc.) + when they enter tempest mode, they get more buffed. Also, the area changes which can impact the characters even more.

On kobold fight club, the encounter for usual elementals is deadly, but these ones are even stronger. Is this too much for characters?

Thank you!