Centuries ago magic flourished on the earth making monsters and spell casters. Three humans stood out from the rest of the spell casters though. One was given the element of fire and could shift into a dragon. Another was given the element of grass and could shift into a grass monster. The last human was given the element of rock and could shift into a boar.
The spell casters could do more than shape-shift, too. The fire spell caster could release any sort of flame from his body. The grass spell caster could control the life of plants and attack an enemy with them. The rock spell caster could levitate and throw rocks.
As the three spell casters walked through an abandoned home, a creature with three heads suddenly appeared. This creature absorbed their powers and has total control over each of their element.
We must become assassins, so we can defeat this beast of power.
The creature used its newly acquired fire to burn the spell casters.
A doctor healed the spell casters but could not get their powers back.
You should be fine now. Your powers are gone and I can not get them back though.
The spell casters decided to train as assassins, so they could slay the beast.