Can the DM choose to always attack me instead of my mount?

Question

I've been trying to work out the whole "Combat while mounted" thing in 5e. My biggest question is this, if I am up against a monster (or a few), does the DM roll to see if the monster will attack me or my mount? For instance, if I am in combat with 3 orcs, do all three orcs just choose to attack me or is there a 50/50 chance that one or more of orcs attack my mount instead?

In the past few combats my DM has targeting my ranger and saying that he doesn't care about my mount. I'm a Halfling ranger mounted on my Wolf companion and I am attacking with both my mount and myself. It just seems that there would be a chance that the monsters would attack my wolf sometimes instead.

Answer 1

Enemies get to say which one of you they want to attack. Usually the mount is easier to hit, but killing it doesn't stop the rider from attacking on foot. Attacking the rider is harder, but more effective if successful (especially if the mount decides not to fight on its own).

The monster is making a tactically sound decision by attacking you, since you are more dangerous and squishier. With the mount, he would have to carve through the mount's HP, and still have to deal with your high DPS after. Also when your HP is low, you might retreat, but if the mount's HP is low at best you'll send the mount away and keep fighting yourself. What you can do is use armor and other means to make your AC higher (even if it reduces your own DPS) while trying to maximize your mount's DPS and neglecting its AC. That way, either enemies stop targeting you like you want, or they still target you but you derive greater tactical advantage. Either way you win.

Your DM could have monsters acquire targets randomly, or have them target based on roleplaying or flavor reasons (eg maybe these orcs just really hate halflings), and not tactics. However, he doesn't have to. Some DMs like to have monsters always act in a tactically optimal way - if you don't like it, you might want to talk to the DM about it and clarify whether combats are supposed to be roleplaying focused, or tactics focused.

Realistically, if one tries to attack the rider and misses, there should be a chance to hit the mount instead. However I don't believe 5e DnD models this by default. Part of the problem is that in DnD, there's no missing - there's only failing to do damage which does not necessarily mean missing: it can mean hitting but being repelled by the armor. Granted, you can also beat the AC but still fail to do damage because of damage resistance on the armor... Best not think too hard on it, but the point is that failing to beat the AC doesn't automatically mean miss.

The exceptions to this are:

• If something moves the mount (like a spell) you must pass a DC 10 Dex save or you will fall off the mount.
• If they knock it prone, you'll have to burn an action on dismounting or be knocked prone.
• If the mount provokes an attack of opportunity, they can use it to attack you instead of the mount.

These aren't really exceptions though, and more to do with special effects. There isn't anything that lets you attack both rider and mount at once (except for area effect spells) or forces you to attack one or the other.

Answer 2

Under the Mounted Combat section of the SRD, it states that

If the mount provokes an opportunity attack while you're on it, the attacker can target you or the mount.

The rules make no mention of monsters being forced to attack one or the other, so they attack at the Dungeon Master's discretion.

Answer 3

We had a similar discussion in one of my groups and we agreed to the GM’s explanation of how he chooses the target on behalf of creeps and NPCs:

Pretty much all sentient beings attack the target first that they perceive as the biggest danger for whatever reason (if they chose to attack at all). A better explanation would be, that they try to eliminate the threat that seems most pressing weighed against how hard it is to eliminate¹.

Depending on their intelligence, tactical sense, personality traits, or ideology they may perceive threats differently than a (hopefully objective) observer:

• A goblin might not have the insight to prioritize the exposed, low AC, low HP spell caster at the back of their enemies’ party.

• A veteran fighter party of average intelligence probably would have that insight especially if they learned how to deal with mages.

• An experienced group of bandits might know that they just need to get to the throat of the weakest member of a group of travelers to coerce the others to surrender their valuables.

• A Good paladin might want to get rid of the undead first before attacking living but otherwise equally Evil enemies even if he doesn't currently have a weapon that deals bonus damage against the former.

• A wild beast may not perceive a mount and its rider as separate beings at all and simply attacks the part that looks the easiest to attack (which may be either depending on the size, armor, and attack types of all three involved).

¹ “That minion may only deal ¼ of the damage of its boss per attack to our group, but its attacks are clumsy and its armor looks cheap and rugged. So I can likely kill it within two rounds, but the boss takes at least 6 successful hits.”

Answer 4

On my opinion, a dog (INT == 1) is already capable to understand that the enemy flock leader should be attacked first [i.e. the human sitting on the horse].

On my opinion, INT == 2 is the limit, from which we can talk about a primitive fight strategy. On INT == 1, the creature will do for what it was trained for, or what his instincts say (what can be also strategic, see how lions are hunting in groups).

The intelligence of these orcs were probably at least 3, being capable to talk. They were also obviously fight-trained. They also knew very well, that after neutralizing the human, they will be able to kill also the horse easily. And, after that, they can eat the brains of both of you, after letting them to rot some days long, to get a better flavor.

What is not clear to me: if your character was a well trained fighter, he should have been able to use the horse to defend himself (and, to help the horse to defend itself).

Thus, on my opinion, it was okay that the orcs focused only to you, but I think you should have got more advantages from the horse fight.