Watch — :Put a +1 firepower marker on another Mech you control.
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Explained
Watch — :Put a +1 firepower marker on another Mech you control.501.6
Exhaust it to use it. Choose another Mech you control when you use it, not this card; without one, it can't be used (301.7d). Markers stay on a card while it is on board, and several add up; it loses them when it leaves the board (301.7). Only in your own watch, with the crossfire empty; it resolves at once. Not in the turn it came on board during a watch, unless it has Quickstart.