Mounting A Creature
To mount a creature:
- You must be within 5 feet of it.
- It must be willing to bear you as a rider.
- It must be at least one size larger than you and have an appropriate anatomy (DM discretion; horse yes, gelatinous cube, probably not.)
- You must spend an amount of movement equal to half your speed; 15 feet if your speed is 30 feet, for example. You can’t mount if you can’t spend this movement for any reason. Dismounting is the same process, and you dismount into a space within 5 feet of your mount.
When Mounted
You can only mount or dismount once per turn, and once you’re mounted, the following rules apply:
- If your mount is a trained one, such as a horse or mule, you choose to either control it, or let it remain independent.
- When you mount an intelligent creature, such as a dragon, it always retains its independence. This also applies for an untrained creature.
- If you control a mount, its initiative changes to match your own, but it can only choose from three actions; Dash, Disengage, or Dodge. It can act immediately on the turn when you mount it.
- An independent mount retains its place in the initiative order, but can take all its actions normally.
- In every case, if your mount provokes an attack of opportunity, the attacker can choose to target either you or the mount, so long as it can reach you.
Merlina the githyanki dragonrider is mounted on her young red dragon Cinder and making diving attacks on a storm giant. Initiative has already been rolled, and since Cinder is an intelligent creature, he has his own initiative. Merlina has a 19, the storm giant has a 14, and Cinder has a 7. On her turn, Merlina readies an action to strike with her halberd when she’s within reach. The storm giant acts, then Cinder’s turn comes up, and he flies in, making his full multiattack against the giant. At the same time, Merlina’s readied action goes off, and she attacks with her halberd. As they fly away, the giant gets an attack of opportunity on the dragon, but decides the rider is more dangerous; he targets Merlina instead of the dragon, and hits her with his greatsword, wounding her severely as the pair fly by.
Disrupting Mounts
Naturally, being mounted carries some drawbacks, as well.
- If your mount is moved against its will, such as by a thorn whip spell while you’re on it, you must immediately make a DC 10 Dexterity saving throw. On a failure, you’re thrown off your mount, and land prone in a space within 5 feet of it.
- If your mount is knocked prone, you can use your reaction to immediately dismount, “bailing out” and landing on your feet within 5 feet of the mount. If you can’t or don’t use your reaction for this, you are instead prone within 5 feet of your mount.
- Apart from this, a DM can call for a Strength (Athletics) check to remain mounted in response to sudden disruptions. Of course, these checks will be much easier with the…
If you’re riding in a military saddle, you “have advantage on any check you make to remain mounted”. Note this doesn’t mention saving throws, unfortunately. Furthermore, if you want to ride an aquatic or flying mount, like a gryffon or a dolphin, you’ll need an exotic saddle instead; prices can be found in Chapter 5 of the Player’s Handbook under Mounts and Vehicles.
In addition, you can also buy barding, which is armor for your mount. Barding works exactly the same as armor for humanoids, but is four times as expensive and weighs twice as much; expect your DM to up this price if you’re buying barding for an especially unusual mount!
But Where Am I?
If you play on a grid, you’ll encounter the question of where, exactly, the rider is on the mount. In the center? Do they share the mount’s space?
The answer in the rules is that the rider is in a space the mount occupies, and can use its own movement to move freely on the mount.
Many people, unsatisfied by this answer, either put the rider in the center of the mount (sometimes placing them on an intersection) or just treat the mount and rider as a single creature that occupies the mount’s space. Any of these three solutions can work, but—and say it with me, folks—talk to your DM and get their interpretation before proceeding. Remember that, for especially large mounts, you may need a reach weapon to even attack from atop it!
Additional Rules
Some other game elements interact with mounted combat in various ways; a few examples are explained below:
- Lance. The classic weapon of a riding knight, the lance is normally two-handed, but can be wielded one-handed while mounted. This technically means you can dual-wield lances while mounted with the Dual Wielder feat. Do with that knowledge what you please.
- Mounted Combatant. Of course we had to mention this one. You gain advantage on melee attack rolls if your mount is bigger than the target you’re hitting; a major boon if you fight a lot of Medium creatures. You can redirect attacks on your mount to you instead, which is great if you’re sick of mounts dying. And creatures you’re mounted on gain the rogue’s Evasion feature. Very sweet all around.
- The Saddle of the Cavalier prevents you from being dismounted forcibly, and imposes disadvantage on attack rolls against your mount. A decent upgrade so your mount won’t have to Dodge so often.
- Cavalier. A bit much to dive into here, but if you’re looking to make a mounted combatant, check out the Cavalier Fighter Archetype in Xanathar’s Guide to Everything.
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