Steve Gorak
Adventurer
From Controlling a Mount (PH 198):
You can either control the mount or allow it to act independently. Intelligent creatures, such as dragons, act independently.
These are 2 separate sentences. The first sentence applies to mounts. The second sentence applies to intelligent creatures. While an intelligent creature can be ridden, they are not classified as mounts, and any attempt to refer to a dragon as your mount may have unintended consequences (eg - being eaten).
1. If the player decides to control their mount then:
It's initiative changes to match the rider
It moves as the rider directs, and can only take the 3 actions Dodge, Disengage and Dash.
2. If the player decides to let the mount act independently then:
It retains it's own initiative
The mount moves and acts as it wishes, which may not be what the rider wants. They cannot choose which enemy the mount targets, which attack it uses, or prevent it from fleeing if it is badly wounded.
I would allow a player to switch between controlling a mount and letting it act independently in combat.
So [MENTION=63746]Binder Fred[/MENTION] if you control Frigate it is as per 1. above. If you do 2. it will be up to me and the horse will act on it's own initiative and potentially attack or do something else.
As a DM liberty a mount can be used to trample when controlled by sacrificing one of the riders attacks (if you only have 1, you lose your attack).
Seem fair?
Definitely, this is what I would have ruled also, but for trained mounts such as warhorses. I doubt donkeys and oxes would willingly trampede enemies. Even an untrained riding hose would be a bit of a stretch...
I also like the image of he warrior that uses his warhorse to push/trampede enemies, and finish them wih the swing of his weapon.
My 2 cents...
Cheers,
SG