Volibear

Dragonsoul Sage enters exhausted like other units, so its one-Energy ability starts helping on a later turn. Mobilize and the Legend instead channel exhausted runes. Those runes can supply Power immediately if recycled, but keeping them gives future turns more Energy. Use Sage to support your Energy payments while deciding which runes you can actually afford to spend. None of that makes a missing Fury payment disappear.

Sky Splitter costs eight Energy and one Fury Power, reduced by your highest friendly Might. A surviving Scorcher makes that three Energy; a nine-Might unit removes the Energy payment entirely. You still owe the Fury Power, and the target must be at a battlefield. Punch First can improve the discount, but paying two Body Power just to save Energy is not automatically a bargain. Challenge offers a different answer: your unit and the enemy deal damage equal to their Mights to each other, and as an Action it also works during a Showdown. Check the return damage before sacrificing the body that was supposed to carry the next attack.

Units normally enter exhausted, so the turn you pay for a large unit is usually not the turn it attacks. Volibear, Furious costs ten Energy and two Fury Power, and his five damage happens when he attacks, split among enemy units at that battlefield; playing him on defense does not fire it. Scorcher has its own cheaper route: Accelerate brings the total to six Energy and one Fury Power and lets it enter ready. Rengar, Trophy Hunter reaches a fight another way, because Ambush lets him enter a battlefield where you already have units as a Reaction. Take the ready body when there is a useful attack, rather than spending the extra Power on a unit you intend to leave at base.