CLAP! Arad put his hands together, glaring at the two with glowing red eyes. "Time to cook."
A spark of flame emerged from his back, the crimson light from it darkening his face to them as the wine barrels in the building burst.
Expansions are the process of releasing one's magic in a violent burst to gain environmental advantage. It is most common with powerful entities with an abundance of mana to waste, such as spirits, dragons, and devils.
The city lord started turning away to run, while the fake Merlin lifted her staff, trying to conjure a barrier as fast as she could.
A water dragon fights best in water, so they would benefit from flooding the battlefield, and their enemies would suffer.
Arad's body burst into flames, and the glass windows of the buildings shattered. The wooden houses around them started smoking.
It's like a candle's last flare, burning a large chunk of the caster's mana to gain an advantage, a path to victory.