Answer: heatup

AnswerCrossword Clue
HEATUPIntensify
HEATUPWarm, as leftovers
HEATUPBecome interesting, like a pennant race
HEATUPWarm.
HEATUPBecome intense
HEATUPGet intense
HEATUPGet more intense
HEATUPUse the microwave, perhaps
HEATUPWarm