Mounted Monsters

[ZenBear]

I've started statting up the Steelhead Mercenary Company (https://warmachineuniversity.com/mw/index.php/Theme_-_Soldiers_of_Fortune) from Warmachine and I've hit a weird spot with the Heavy Cavalry. Here's the rough draft:

Steelhead Heavy Cavalryman
Steelhead Mercenary Companies often include hardened horsemen, providing the speed and power of heavy cavalry at a reasonable price. Though they demand more than Steelhead infantry, employers consider the horsemen a bargain. The cavalrymen have a reputation as tough veterans who seek out the greatest risk because it brings them the best pay. Though some citizens in war-torn areas accuse them of banditry and looting, Steelhead officers insist their men are professionals who take only the normal liberties expected of any red-blooded soldier in a time of war.
Medium humanoid, neutral
AC: 16 (ring mail & shield) HP: 44 (8d8+8) Speed: 30 ft. (60 ft. while mounted)
STR: 14 (+2) DEX: 14 (+2) CON: 12 (+1)
INT: 10 (0) WIS: 10 (0) CHA: 8 (-1)
Mounted Combatant (Riding Horse): The cavalryman rides a Riding Horse with a speed of 60 ft., which attempts to flee if its rider is incapacitated. While the cavalryman is mounted, the mount may only take the Dash, Disengage, and Dodge actions. The cavalryman has advantage on attacks against unmounted creatures that are smaller than its mount, and can force an attack targeted at its mount to target the cavalryman instead. If the mount is subjected to an effect that allows it to make a Dexterity saving throw to take only half damage, it instead takes no damage if it succeeds on the saving throw, and only half damage if it fails.
Flank (Steelhead Halberdier): The cavalryman has advantage on an attack roll against a creature if it is within reach of at least one steelhead halberdier that isn’t incapacitated. If it hits with a cavalry axe attack it deals an extra 5 (2d4) damage.
Relentless Charge: If the cavalryman moves at least 20 ft. straight toward a creature the cavalryman ignores difficult terrain during the movement, and if it then hits the target with a cavalry axe attack on the same turn, the target takes an extra 2 (1d4) damage.
Actions:
Blunderbuss: DC 12 Dexterity save, 5 (1d6+2) piercing damage, range 30/60 ft.
Cavalry Axe: +4 to hit, 6 (1d8+2) slashing damage.
CR: 1

I'm trying to stay as true to form as I can, but it's really limiting and forces me to make weird combinations of features that don't work the same way in D&D as they do in Warmachine. A lot of the cavalryman's power is contingent, and when the conditions aren't met they're fairly underwhelming for their CR. It's also quite a wall of text for a stat block.

[BerzerkerUnit]

I'd make it one Large creature

Remove the mounted details, just give it a speed of 60 and bonus action dash, disengage, and Reaction parry, and evasion (all representing the mount doing stuff for the rider).

Allow some mechanic (50% hp, crit, knock down) to half speed, reduce to medium size, and eliminate the bonus actions as the mount is slain or flees.

Good luck!

[Ninja_Prawn]

It's tough. Whenever I've implemented mounted NPCs, I've considered them to be two distinct creatures that happen to be deployed together. Both mount and rider have their own stat blocks and a CR that is not changed by the fact that the rider is mounted, since the encounter building mechanics already assign a multiplier for the effective challenge of monsters based on how many there are. Clearly that's not ideal in this case though...

[BerzerkerUnit]

My recommendation is rooted in ease of use. They get some solid benefits but those can be taken away (automatically at 1/2 hp or by meeting some other condition, like catching them off horse).

It negates having to track hp and defenses for two targets, especially challenging when a cavalry force might have 12 units. It also eliminates X amount of prep wasted when wizard fireball eliminates all horses in round 1 reducing most of these guys to what looks like Veterans.

I see this in a lot of the humanoid monsters, their CR is based on a variety of factors, but in most cases, disarming them transforms them into Boppo the clown, just waiting to be knocked over again and again as their damage goes from 2d8+4 (Ogre) to just 5, maybe d4+4. I digress.

Good luck!