Roll a d100.
Say "The ants go marching <result> by <result>."
Now finish the rhyming couplet with a sentence about "the little one"-- e.g. if the ants go marching 6 by 6, perhaps "the little one stops to take a piss".
Every syllable of the number must at least slant rhyme.
Roguelike mode: Set a timer for 5 minutes. Roll d100 the first time, 2d100 the second time, and so forth. Keep track of your high score.