The Flame Command is a Sidekick Command that Tricky learns in DarkIce Mines during Star Fox Adventures. It's used to do a variety of things such as to throw fire at enemies, to turn on campfires, and to melt ice. It can be accessed through the C Stick Inventory, and so it can be assigned to the Y Button, like every other Command.
Tricky learns it in DarkIce Mines from a SnowHorn Fox McCloud has to save from two SharpClaws shortly after using the first Bridge Cog. After Fox has beaten the SharpClaws, the SnowHorn merely says "I see your young friend has yet to learn his Flame Command. Go on youngster. Give it a go." and Tricky learns it. After this, the SnowHorn offers to help Fox through the main gate, if he is brought two Alpine Roots.
Like the Find Command, Flame also depletes the Tricky Energy meter, by the speed of one fifth of the meter (or one Blue GrubTub Fungus) per Flame. If the meter is empty, Tricky won't follow Fox's Find and Flame Commands until he is fed more GrubTubs.
If Fox hits Tricky enough times with the staff, Tricky will use the flame command on Fox and attempt to burn him. This does not deplete the Tricky Energy meter.