What is the range when using Ocean’s Might 3-4 dice result?

As this damage is dealt to a target, you would use the Range of the unit dealing the damage.


Does the tridentholder itself take damage for Ocean’s Might 5-6 dice result?

No, as Possess Power says that the tridentholder ignores damage it is dealt by units. The tridentholder also gets to keep its trident after this damage since it is the unit that dealt the damage.