I just got the Sacred Pool expansion which adds a bunch of war horses to the game for the Dread Knight's sake. If you obtain two war horses, is there any reason their effects would not stack? May I add my craft to my strength in battle twice?
Flavorwise, the idea of riding multiple warhorses definitely falls flat. However, there is nothing in the rules indicating that only one is allowed at a time. The power is held somewhat in check due to a single loss of life in battle/combat resulting in losing all of the Warhorses.
While not answering for this specific card, the FAQ indicates that multiple "Add Craft to Strength" effects can be applied to a single battle:
Q2: Can the Monk use his inner belief to add his Craft value to his Strength during battle and then cast the Psionic Blast Spell to add his Craft value to his Strength again during the same battle?
To alleviate the flavor concerns, I like the response from this FFG Forum Post:
It seems to me that many people think it's weird because a human being can only be mounted on one horse at any given time. While this is true, who says that the player is mounted during combat? Sure it makes the most sense, to have the horse biting and hoofing while its rider slashes with his or her sword, but there's no reason that a well trained warhorse couldn't be flanking and opponent with its faithful companion. When you consider this, two horses, or three or four or whatever, are irrelevant.
But this is all superfluous, anyway.
It only makes sense that you could ride only 1 horse at a time, so I think you could only use 1 in battle. However, I imagine the second horse could be walking behind you, so it would still count for anything that affects followers (e.g. You could still discard the horse if you Suffer Blood Loss at the Vampire's Tower in the Inner Region).