At all cost
"Some fights will just get you bloody"
The snake has the following description:
For the linked troop : +1 Movement Capacity Cancel any other creature effect in Battle.
Polyphemus travels with seven troops so he will not be affected since travelling occurs outside a battle. Only the Strenght bonus will not be affected.
For the kraken it will cancel the strength bonus
Cereberus would not be attachable since moving troops occurs before the battle
The two extra units are a battle enhancement,when battle occurs, which would mean they're not included in combat.
Cerberus is questionable with the looked up wording. I'd have to see the text on it, but I suspect you cant attack it.