Oh, I know this one, but there's a story.
Fire elementals.
Hold up, what do you mean, fire elementals? They're so generic. They're just fire wandering around. They're neither common enough to be familiar, nor exotic and wonderful enough to be really special. They're high enough level to not be a beginner encounter, but not high enough level to matter for your legendary heroes. Why would you pick the generic 5e
Fire Elemental? Not even the Fire Elemental Myrmidon (which, if we're being honest, is much cooler)? And why fire?
I was in a campaign where my character was a druid. I say was because there were some party issues. Basically, another player decided to bully my character because of his alignment, which he never acted on in a way his character could even possibly know. Basically, the goodie two-shoes fire sorcerer/paladin multiclass munchkin chosen one hated the maybe kind of evil, grumpy druid who was really just angry at Drow all the time. Genocidally (and evilly, hence the alignment) angry. So, much to my chagrin, my level 6 druid retired from the party after constant feuding with the paladin, and I substituted in a much less interesting character for the next several months of the campaign.
Until...
About three or four months and several levels later, our characters found ourselves in an arena on a pirate island. Each character had to engage in a death match for the sake of a shiny plot McGuffin, with the pirate team (or heroic adventurers) who had the most individual wins taking the item. All the other players and my new character won, with varying degrees of ease. I think I had three HP and one spell slot left at the end, which was not much for level 12. The paladin steps into the arena for his fight, and I receive a familiar character sheet from the DM. Guess who the sorcerer paladin munchkin was fighting?
Now, my druid had been off murdering Drow, so he was also leveled quite a bit from when we last saw him, but this multi-class monster was overpowered. Like, actually breaking the rules and taking advantage of the relatively inexperienced DMs (we had two rotating DMs) to get away with power-gaming shenanigans. This character was the brainchild of the best player I've ever met, who can make *ANY* character or build incredibly powerful while still having a great story and personality, and a newbie who simply fudged and bent things using his advice and his own lack of experience to get away with "Oh, I didn't realize that worked that way" (followed by DMs allowing his BS because they didn't realize how broken it was getting, and finally realizing their mistake too late to rein in the awfulness- and I don't just mean that to be rude, he legit abused his backstory to basically give himself a private religious order and his character may have been a demigod, divine intervention included).
This is the stereotypical "fantasy-writer-turned-player" who dominates the campaign around things that just sort of aggravate the DMs, to the point of telling them that things didn't actually happen the way they said it did and, for example, trying to conjure allies and abilities from his backstory, doing things without making checks or running things by the DMs which domineered the campaign, and the like. It wasn't just me getting frustrated by it, and his at the table behavior made us more frustrated. He would show up irregularly without notifying anyone when he was gone, he would zone out when anyone else was playing, and his character would judge other characters for things he couldn't have possibly noticed, such as when the party was split, because, spoiler warning, his character was a demigod (according to him, at least).
So, when my newly leveled druid stepped into the arena, I was still pretty much guaranteed to get slaughtered. Circle of the Moon druids are powerful, but their weakness is sustained fights at that level, and between paladin and sorcerer features, this abomination had more armor, more effective health, more spell damage, and generally just better stats across the board. I could have probably won had we been at level cap, but I simply lacked a killer feature to counter his balance of durability, damage, and annoying spells. However, he had one weakness.
He was almost entirely specialized into doing fire damage. His spell list (somewhat unbeknownst to me, as I only really saw him use the same four spells for damage) was almost entirely fire damage. No control spells, no defensive spells, only fire damage spells. His feats were fire damage feats. His entire character gimmick was burning things. So, when the fight began, I scrambled for one thing: Elemental Shape: Fire Elemental.
After a devastating damage spike at the start of the match, as he burned his highest spell slot and some sorcery points to try to nuke my druid in one shot, I moved towards him and announced my bonus action: Elemental Shape. Queue a sorcerer/paladin munchkin desperately trying to kill a fire elemental, loaded with HP, while doing absolutely no damage with his fire spells. It was still a close battle- having convinced the DMs to let him alter his stat block, get more HP than he should have, and being min maxed with feats and abilities, it was still a powerful character.
However, he ultimately succumbed to the unrelenting flames, once again leaving me with very little HP (in elemental and druid form- guy won initiative and almost one shot my druid before I could enter elemental shape because it was a broken build, produced by the min-max prowess of the best power gamer and character builder I've ever met and the unhinged imagination of a self-insert fan fic author) and I celebrated my (much belated) vindication.
I still smile when I think about fire elementals, because I remember my victory over a particularly egregious table rival.
To be fair, the DMs were going to force him to retire his character after the session anyway, because they found out it was technically not rules legal (his character failed the multiclassing requirements and they found out before the session), but it felt good to have my character who I retired to keep the table from devolving into bickering vindicate himself in the arena. It is my only player kill, and I don't really regret it. And that is why I have a warm spot in my heart for Fire Elementals.
Thank you for coming to my TED talk.