Originally Posted by
Chronowraith
Except the eagle is a monstrous beast and the BRB states that monstrous beasts acting as a character mount work like monstrous cavalry. It is an awkward situation that GW will have to FAQ because right now, the rules don't support it.
Also, you wouldn't use 4 wounds for this mount as, again, the BRB is specific when it states that the highest value for Wounds (and toughness) is used. That means the highest single value. The twins are both 2 wounds each while the eagle has 3. So according to the rules as written (since nothing in the twins entry countermands this) you are stuck with 3 wounds.
Again, I think GW dropped the ball here. The rules simply don't make sense as written because if you go with the eagle you are losing out on the twins unique rule (and a spare wound).