I actually have a player that complains if there are no options for using the environment to do damage. Great topic 👌

My favorite environmental kill is still the defining moment for my character's relationship to our city in a high-magic campaig, which happened fairly early. My character (Woodelf Dreams Druid) is essentially a cross of The Flash & V (for Vendetta) who wants to have magic freely used by all. When the party went to confront the evil mayor at the top of his tower, like you do, whe got him to confess being in the main evil cult & he began to try & kill us. When he saw that wasn't working (even though we were convinced he killed the bard) backed up, smiled, & threw himself out a window. But remember, I'm a Faceless background, a D&D superhero, so jumping though windows is my thing. I follow after him & skydive to catch him. When I do, the guy (poorly) slits his own throat with a knife he knows I have a copy of. It hits me that he's trying to blame us for this. He's clearly full evil. So I let go of him & cast gust of wind, propelling him to the cobbles below, mangling his body & actively killing him to frame his kiling of himself to frame us for murding him as at least a tragic accident I tried valiantly to prevent, though I waa too late. & it worked. The guards only could see the impact wounds & my performance convinced them we did not push him. And that's how I became enemy no. 1 for the cult.

Had one in a recent session of one of my Frostmaiden games. The party's barbarian sparta-kicked the duergar warboss into the trough of molten lava they were powering their forges with.

Even mundane environments, like bodies of water, pits of mud/offal, or even large swathes of sand, can be hazardous if used creatively by the players or the DM.

Engagement for the engagement god!

This is a little off topic, but I love your makeup! More on topic, I always make sure to have some sort of dangerous or potentially dangerous thing in the environment for both the players and the NPCs to use. One of the most exciting fights I ever did was a boss that pushed and pulled everyone in the room, with the edges of the room covered in lava. Some people got rather singed by the end of the fight.

One of the best in a story is how Corwin beat Benedict by using a patch of grasping grass to manuever him into range. I used this idea a couple of times in Amber Diceless and other games.

We had a evil mage casting spells on a 60’ cliff. The barbarian did the math, grabbed the mage, and jumped off the cliff.

Favourite environmental kill? Following up a divine smite with a shield bash to push a troll off a cliff, the bottom of which was covered in a Spike Growth from our druid. ^^

Honestly, there are not enough wall spikes out there.

Sickening Radiance is pretty sick too.

I quite liked using Gravity Sinkhole to pull Auril into Ythrin's Mythallar in IWD

environmental kills are great, I was on an airship and ruined an encounter or my DM because I grappled and dragged them to the rail and just tossed them over

Haha, perfect picture

People like to complain about PC races with fly speeds. It's funny that Todd touched on one of the best ways to trip up a flying PC. Make a dungeon designed by a mad graviturgist, line the ceiling with stalagtites, and pepper the large chambers and halls with random reverse gravity fields the start ten feet off the ground. The flying PC will be more careful after the 5th time they fail a Dex save and fall 50 feet upwards into a vertical shaft capped with spikes pointing down.

I have placed a save on that in effect in my campaign (Str bonus/penalty apply)

Eldritch blast doesn't pull or push people it just does 1d10 damage on spell attack

Problem with a lot of environmental damage is by the book their damage sucks compared to just doing something else. Obviously Todd listed some of the best of the best of environmental damage. But if you drop a stalactite on someone or the like, its damage is weak and could have done more simply hitting them with the spell or explosive arrow you used to knock down the stalactite. Yes you can house rule them. I do because I want to encourage creative gameplay. However...many game tables stay closer to by the books