Giant Lynx, Mammoth, Manticore, Masher, Mastodon

 AD&D Giant Lynx

 

don't sue me TSR games I own the monster manual and can show it to people if I want...!

AD&D Mammoth, Mastodon
These nearly identical entries (Mammoth has 13 HD instead of 12, does 3d6 instead of 2d8, and has AC 5 instead of 6) take up a good half of a page and are largely redundant with the Elephant entry earlier. More and more evidence for the existence of someone very interested in finicky details of the pleistocene being involved with early D&D.

AD&D Masher
Probably among the most forgettable monsters of all time, these are 8HD 'worm-like' fish, dealing 5d4 damage and being covered in poisonous dorsal spines that mean it must be attacked from the front or below, lest the spines fend off attackers who must either abort their melee attack or save vs poison or die. They eat coral but are prone to attacking if surprised or threatened in "self-defense." It's not a bad concept for a monster, though it being underwater and just a fish limits the need to engage with them.

One might expect them to be popular sources of poison spears by the underwater races of Sahuagin and so on, but I see no mention of interaction with other sea creatures. In fact, apart from a lonely 2e wiki entry and a mention of dwelling in the waters of Raven's Bluff in Toril, they do not appear to have any internet presence.

Some random 5e character named Masher has about the same online presence as this fish on search engines

AD&D Manticore
An interesting creature, it can fire 4 volleys of 6 spikes, dealing 1d6 damage each at the range of a light crossbow. As they can fly, one assumes they soften up or slay foes at range, then close in to finish off whatever remains with their unimpressive melee (a regular ol lizard man is about equivalent if you ignore the HD difference) Their treasure type E is typically unimpressive- there is a chance of something good, but it is a low chance indeed. If nothing else, their iron tail spikes can no doubt double as iron spikes to shut doors with.

Manticores are an interesting tactical problem for low to-mid level parties- one must survive the volleys of fairly accurate (+6) spikes, then be able to defeat the creature before it flies away to end its aerial reign of terror, or find a way to track a flying beast back to its lair for treasure. They are of low intelligence but are 'Lawful Evil' which might imply deals can be struck with them, though it is unclear if they speak despite having human heads.

Sunset Realm Giant Lynx
Like most giant animals, the answer is 'sure, why not, there are many ways to become gigantic.'

nasty man

Sunset Realm Mammoth/Mastodon
See the Elephant entry. Most of them are found in the frozen lands of Fomoria south of the fault, driven ever further south by Deadliege expeditions to steal their bones and make necromantic war-constructs from them, just as what was done to their less-hairy elephant brethren in the warm north jungles.

Lungfungus had an interesting approach for these beasts statblock wise that I think I'll steal- failing a melee attack against one incurs 1d8 damage from trampling, as an automated way to make unskilled hunters better off on ranged duty and account for the bulk of the beast simply trampling people.

Sunset Realm Manticore
Goblinpunch already did a pretty great take which I am mostly stealing from.

Manticores are Nightmare creatures, born of dreams of spite and grudge. As Nightmare is closest to the waking world in Saresare, they are known to be residents of that desert sultanate, though they are often hunted and driven into Yuba, Fassulia, and Mercia, cursing all the way. Their faces are that of the host of the nightmare that made them.

They eat hard things, breaking their teeth and bleeding their gums, and incorporate those things as their tail spikes. Shards of bone, stone, and metal compose the quills of a manticores tail. Vomiting forth unsuccessful consumption leads to their lairs being foul smelling and messy, and frequently haunted by unclean spirits of disease. Harpies and manticores do not get along well, but are frequently found together regardless. They fear sphinx.

Manticores are generally unreasonable, growing more resentful of everything you have that they don't but can be satiated temporarily with slander and general nastiness. Politeness and care only pisses them off more. Aiding them with whatever grudge they are nursing is the only way to be allied with one.
If a manticore cannot kill you, it will follow you, harassing your friends, scaring off game, leading enemies to you, and worse if it can manage it.

If you are hit by a manticore tail spike, it embeds in you and you become poisoned by hatred. You cannot aid other people, and can only laugh at their misfortune, mocking them, listing out all your grievances and resentments towards them. Pulling out a spike deals 1 extra point of damage per spike, and you can pull out any number within a round as a full-round action, but someone with a spike in them certainly can't pull spikes out of someone else. Those who die, not from the manticore itself, but from the side-effects of this poison, will spawn a Nightmare incursion upon death which in turn will spawn manticores with their face. Manticores try to engineer these scenarios, knocking people off cliffs and then poisoning their friends and similar so they let them fall.

This poison is nightmarish in nature and only takes effect when the manticore hurls spikes, it can only be collected by things that can collect dreams or emotions.
Similarly, only their spikes are real- upon being slain, the manticore collapses and turns to nothing. Manticores do not have biology or ecology, and could indeed sit in a dungeon room for 100 years doing nothing but hoping to eat the next person they saw.