Rally — Whenever Firemantle Mage or another Ally enters the battlefield under your control, creatures you control gain menace until end of turn. (A creature with menace can't be blocked except by two or more creatures.)
If a creature with a rally ability enters the battlefield under your control at the same time as other Allies, that ability will trigger once for each of those creatures and once for the creature with the ability itself.
Multiple instances of menace on the same creature are redundant.
When an Ally enters the battlefield under your control, each rally ability of the permanents you control will trigger. You can put them on the stack in any order. The last ability you put on the stack will be the first one to resolve.