Choose one —
• Gain control of all creatures with power 4 or greater until end of turn. Untap those creatures. They gain haste until end of turn.
• Gain control of all creatures with power 3 or less until end of turn. Untap those creatures. They gain haste until end of turn.
Gaining control of a creature doesn't cause you to gain control of any Auras or Equipment attached to it.
Mob Rule can affect creatures you already control or ones that are already untapped. It will untap them if applicable and give them haste.
Once you gain control of a creature, it doesn't matter what happens to its power.
You choose which mode you're using as you cast Mob Rule. Once it's cast, you can't change its mode, even if creatures' powers change in response.