Answer: heatup

AnswerCrossword Clue
HEATUP

Intensify

HEATUP

Warm, as leftovers

HEATUP

Become interesting, like a pennant race

HEATUP
Warm.
HEATUP
Become intense
HEATUPGet intense
HEATUPGet more intense
HEATUPUse the microwave, perhaps
HEATUPWarm