A reference to the “least powerful” creature refers to the creature in play with the lowest power. If there are multiple creatures that qualify, each is considered “least powerful.” If an ability requires the selection of a single least powerful creature, and multiple creatures are tied, the active player chooses one.
Groups of “Least Powerful”
If a card effect refers to a group of “the X least powerful” creatures, it is referring to a number of creatures in play that have an equal or lower power than every creature that does not belong to that group. If there are not enough creatures with the lowest power to fulfill the group, then a creature with the next lowest 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.