Can a mount with the Trampling Charge trait use the bonus-action attack against prone targets?

Question

I'm here with a rather nitpicky question.

We all know that when you have a regular mount in 5th edition, you can't make it attack while controlling it.
But what happens if the mount could attack as a bonus action, as per the second part of a warhorse's Trampling Charge trait?

The description of the warhorse's Trampling Charge trait says:

Trampling Charge. [...] If the target is prone, the horse can make another attack with its hooves against it as a bonus action.

So this is where I'm going:
We have a shield-bashing Paladin who often knocks opponents prone in combat. If I then move towards said prone opponent, could I have my warhorse attack using its bonus action?

The mounted combat rules don't really say: "You can't use bonus actions". All they mention about actions under your control is: "[...] and it has only 3 action options: Dash, Disengage, and Dodge." In every way, this doesn't seem to tell me that if my mount gets a possible bonus action (which might be an attack), it wouldn't be able to perform it under my control.

In the rules on bonus actions, there is this mention: anything that deprives you of your ability to take actions also prevents you from taking bonus actions. But I'm guessing this has nothing to do with specific actions, but rather conditions like paralyzed.

So what do you think? Is this legit?

Answer 1

No, it can't make the bonus-action attack in this case.

Trampling Charge is an entire feature – the second sentence hinges entirely on the first; you must make the hooves attack in order to get any of the other benefits. However, if the target of the hooves attack were already prone, then a) the saving throw to avoid being knocked prone is moot, and b) it gets the bonus-action attack automatically.

None of this can happen unless the horse is acting independently – which is only possible if it is intelligent and you let it act independently when you mount it. Whether a warhorse with an Intelligence score of 2 counts as "intelligent" is a DM call.