About non-sentient creatures, animals or monsters, we have to remember they have got better senses. This is really important in stealth operations. An ordinary horse in a night camp could listen or smell a potential predator or a forest goblin trying to steal.
Or a bird could be used to leave a stone with a teletransportation rune on a window in the top of the tower, or to cross a room without touching walls or floor to avoid traps.
You have forgotten in the real life chimpanzee are strong as two humans, and a gorilla as eight. If we talk about elephants then the difference is higher.
Usually animals as companions are too claustrophobic to enter dungeons or underground zones. And if they are barefoot then traps on the floor are more dangerous for people who wear shoes or boots.
Haven't you noticed the great potential as gold reef the subgenre of collectable monster battle arena (Pokemon, Digimon and company)?
A Monnote short for "monster", as in Pokémon (Pocket Monsters) and Digimon (Digital Monsters) is a creature, generally summoned by magic or sufficiently advanced science means, which fights on behalf of its summoner. This allows …
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A type of character who uses the assistance of an animal, Beast of Battle, force of nature, or just some sort of not-highly-sapient creature (with free will) to help them fight. There are a few variations to this: The creature in question has …
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When your setting features snarling, ferocious beasts with names like Fluffy the Terrible, call in Alice the Fluffy Tamer. She'll turn that man-eating, three-headed dog into a precious puppy by sundown, and the hardest part of the job will be …
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A character keeps as a pet what would normally be considered (and the same species may be in every other instance) a bloodthirsty monster. Such a creature may be given a deceptive name. A person with such a pet may be a Fluffy Tamer, if not The …
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The default mascot of The Team and usually the most outlandish of the bunch. Can be a robot, magic animal, or in a more realistic setting, a little girl much younger than everyone else. Often a Sidekick Creature Nuisance. Most of the time, the …
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Where monsters in RPGs can be recruited to fight alongside the heroes. Allied monsters can be individual characters (Paper Mario) or not (the Dragon Quest series to an extent). In the latter case it's common for the monsters to appear "in the …
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This is not only D&D. Here also some old ideas from other Hasbro franchises could be recycled for a new line.
* Edit.
A monster pet tamer class is a serious challenge for game designers, because it has to be original, and the right balance of power to avoid abuses by munchkins, not only by PCs but some DMs.
WotC doesn't need a copy of the summoner class from Pathfinder. They can add its home-grown things, for example points to "buy" monster traits (
demonbinder prestige class from "Drows of the Underdark"), a summoned monsters with chakras (body slots) for a soulmeld class close to the totemist, or a special ritual to summon "eidolons" like the game mechanic for vestige pact magic.
* I like the idea of a gnome as monster-tamer riding on an ogre's shoulder's who is screaming "HOLDUR, HOLDUR!"