Capítulo 154: Finally Done With The Second Stage Of Training.

Then he moved on to amplification casting. The art of casting multiple spells and linking them so that act on another and create an amplification effect. It can be within the same spell which is easier or between different spells which is more difficult. 

Fireballs can be amplified by air gusts or wind cyclones. It can also be amplified by another fireball spell. The more similar spells combine, the more unstable the spell becomes, but it is still easier to amplify a spell with another exact one than a different spell.

It is worthy to note that some spells that can't be multi-casted can be used in a delicate combination to amplify each other. They can't be savages at the same time but they can be cast one after the other to amplify their effects. It's all about timing and coordination.