Hey Guys...
I love the idea of big Yann mowing down our enemies with his horse, but I thought there was something fishy action-economy-wize. I looked into it and I don't think it is allowed for a warhorse. Dash, Disengage, and Dodge are the only actions it can take when it is controlled by Yann.
This is from the phb page 198 (copied from the SRD, so no IP infringement):
[sblock=Controlling_a_mount]
While you're mounted, you have two options. You
can either control the mount or allow it to act
independently. Intelligent creatures, such as dragons,
act independently.
You can control a mount only if it has been trained
to accept a rider. Domesticated horses, donkeys, and
similar creatures are assum ed to have such training.
The initiative of a controlled mount changes to match
yours when you mount it.
It moves as you direct it, and
it has only three action options: Dash, Disengage, and
Dodge. A controlled mount can move and act even on
the turn that you mount it.
An independent mount retains its place in the
initiative order. Bearing a rider puts no restrictions on
the actions the mount can take, and it moves and acts
as it wishes. It might flee from combat, rush to attack
and devour a badly injured foe, or otherwise act against
your wishes.
In either case, if the mount provokes an opportunity
attack while you’re on it, the attacker can target you
or the mount.[/sblock]
Additional reinforcement/me overselling:
Jeremy Crawford's take on warhorse actions. Please take note of the "
instead" in the answer. In case you're wondering, he's the lead game designer for 5e.
A 2 Int warhorse, if acting independently, would likely go to a meadow and eat grass instead of fighting. Now if Yann finds himself a dragon to ride, that would be a different story, but the dragon would do what it prefers, rather than only take the rider's orders...
I'm sorry [MENTION=63746]Binder Fred[/MENTION], I hope you won't hold a grudge...
Cheers,
SG