Continuing with the assumption that the slash represents the word “or”, today’s choice between elemental or plant leaves me a wee bit conflicted. I like both elemental and plant monsters. I probably use elementals more than plants, but I did once write a dungeon crawl that included every single plant monster in both the Monster Manual and Monster Manual II (counting fungi as plants, of course).
As a player, elementals have been memorable foes and useful tools. Once upon a time, Lord Korbok was operating in fighter mode (wearing his magical platemail, wielding his magical battle axe, forgoing most of his thief abilities, et cetera). Fred gleefully threw a fire elemental at us. Korbok quaffed his potion of speed, went into two-weapon fighting mode, and tore the elemental apart in a single round. It wasn’t quite what Fred had pictured.
Another time, during a game played when I was stationed at Fort Bragg, North Carolina, I was doing something rare for me, which was playing a magic-user. Our PCs were supposed to put a stop to some pirates. We’d tracked them back to their island lair. Most of the party moved forward across the wooden piers to engage the pirates in a surprise attack. My magic-user hung back among the barrels and crates. The surprise attack didn’t work well. I asked the GM what was in the barrels and crates. He told me. My magic-user called for the retreat.
Our PCs raced back to our small boat. The pirates surged down the pier to their ships. Fear was expressed that we’d never be able to outrun the pirates.
“Don’t worry,” said my magic-user. “See those barrels?”
“They’re full of oil,” said my magic-user.
Then my magic-user screamed out the command word for the iron flask he’d hidden among the crates and barrels, thereby releasing the berserk 24-Hit-Die fire elemental from its magical prison. It burned the pirates’ pier and ships while we rowed away laughing.
But I digress. I’m supposed to be picking a favorite elemental or plant, and so I pick the dreaded shambling mound. (Nota Bene: Click the pic for 25% embiggening.)
The 1E shambling mound was a brute. Low AC, crushing attacks, high-ish Hit Dice, half-damage from weapons, resistant or impervious to our best attack spells, and that’s not even mentioning its gruesome suffocation ability.
Get clubbed for 4d8 points of damage in a round, and then smother in entangling vegetable goo 2d4 rounds later! What fun!