A reference to the “most powerful” creature refers to the creature in play with the highest power. If there are multiple creatures that qualify, each is considered “most powerful.”
If an ability requires the selection of a single most powerful creature, and multiple creatures are tied, the active player chooses among the tied creatures.
Groups of “Most Powerful”
If a card effect refers to a group of “the X most powerful” creatures, it is referring to a number of creatures in play that have an equal or higher power than every creature that does not belong to that group. If there are not enough creatures with the highest power to fulfill the group, then a creature with the next highest power is eligible to be considered a part of the group. This continues until the group has been filled or there are no creatures remaining. If at any point multiple creatures are tied at the same power that could qualify them for the group, but there is not enough space in the group for each tied creature, the active player chooses which of the tied creatures are part of the group.
Example: Tom plays the action card Three Fates (COTA 071) which reads, “Play: Destroy the 3 most powerful creatures.” In play there is an 8 power creature, a 7 power creature, and two 5 power creatures.
Tom must select 3 creatures to fill the group and must choose the 8 power creature as the first creature for the group. There are no other creatures in play that are tied for most powerful. In order to fill the group the next most powerful creature is selected, the 7 power creature. After this creature is selected, again there is no creature in play that is tied at 7 power, so a creature from the next highest power must be selected. Tom thus must choose one of the 5 power creatures to complete the group.