Quick Monster Generation

"You're walking through the misty woods. The canopy blocks out the light from the sun but its heat still oppresses you. The Elf stops the party and listens to the wind. 'We are not alone, my friends.', he murmurs as his eyes scan the environs. The party steels themselves for a fight, when out from the shadows leap three large monsters with sharp claws and even sharper teeth! One of them lands two strikes upon the Halfling, grapples her, and then proceeds to bite down!-

"Ah man! Another bear? Why do we keep fighting these things? They just are bruisers, no finesse! C'mon Steve, can't we deal with weirder stuff?" - The Elf

"Shuddup, dood! You try running at game at the last minute with zero prep! You guys wanted to go off the rails and not follow the map to the dungeon! I couldn't think of a cooler monster in time to throw at you." - Beleaguered DM

One complaint I hear and read about in fantasy TTRPGs is that most monsters just feel like "sacks of HP" and aren't mechanically interesting. One symptom of this is Jack Guignol's excellent article "Just Use Bears". Instead of spending a chunk of time and creativity on new monster stats, just reskin any of the Bear creatures from your favorite collection of monsters and throw it at the players. While this is great when you need a creature quickly, I found that it doesn't create compelling enough scenarios to fill more then that occasional encounter.

That's why, with the inspiration from this post on /r/osr, I created a D50 table of unique abilities for creatures.

Show Me the Table!

Here's two examples of creatures created with rules from the table. First up, Flyguys! Miasma and Monster's equivalent to goblins. These guys are 3-5' tall, bipedal flies that can fly up to 5' off the ground. They all prefer to use blunt weapons because they like to exact revenge on humans for swatting and squishing their ancestors for eons.
 

One thing to note before reading these stat blocks: in Miasma and Monsters for every 3HD a monster has it gains an additional Action, while PCs get an additional Action every 4 levels.

Lesser Flyguy

1 HD, AC 11, They wield extra light weapons and slings, mv 40 (35' flying), morale 7 (9 with Flyguy King), initiative 10
# Appearing 2d4 (6d10 in lair)

Flyguys can use their limited flight to their advantage to stay out of melee range of the players and when in their lairs, they will make the players subject to many traps that the flies are all but immune to. They are a very simple example, so let's look at two that are more interesting.

Juggernaut

Bipedal rhino with a near impenetrable shell. Has a single weak point, its neck.
HD 6 + 1, AC 23 (Back of head AC 16), slam (1d12), Mv 30’, darkvision 60’, morale 8, initiative 10
To target its neck, you must do a Called Shot (outside of Miasma and Monsters, up to DM's discretion)
# Appearing 1d4 (2d6 in lair)

These tough guys have really thick hides necessitating some strategy to find their weak point and exploit it! The usage of two Actions allow them to knock the players around, throw them, and generally clobber them effectively. Get enough of these Juggernauts faced against the players, and they'll be running scared to rethink their strategy.

Hanging Tree

A large, old tree that was used so much for hangings that it become possessed by the spirits of the executed and now roams the wilderness looking for new creatures to hang from its many vines
HD 7, AC 13, bite (d12 damage, advantage on creatures that are grappled), vine whip (15’ range, 2d6 damage, 17 Skill save or become grappled), mv 30’, morale 10, initiative 9
When motionless, it looks like an ordinary tree inundated with vines. 17 Mind save to notice that its awakened.
Has 2d6 vines it can use to grasp creatures.
Each vine is AC 15 and has 1 HP
Grappled creatures take ongoing 2d6 damage at the beginning of the Hanging Tree’s turn.
Takes double damage from fire. Morale becomes 7 when it is near fire, and must make a morale check if hurt by fire.
# Appearing 1d2

Now we're talking! A tough creature (though low AC and a clear weakness to fire), it's got 2 Actions, increased range with the vine whips, and can disguise itself as a tree with ease. It normally has good morale, but when it sees fire it will likely run for its life!

Please feel free to use this table in your own games and let me know what you think! I'd love to see what kinds of horrible monsters you are able to create.