Yes, the answer is Sangan. To fill in the rhyme, use the word "Critter," which is the name of Sangan in Japan.
- The eyes have it, so do the toes = 3 eyes, 3 toes per foot. Sangan is a 3-Star monster.
- 9 loves it twice = 3 x 3 is 9
- Good, bad, ugly; Greg, Peter, Bobby; Marsha, Jan, Cindy = groups of 3
- Fiendish clue = Fiend-type
- Good things (and bad things) come in it = 3, or so the expression goes
- The syllables "San" and "gan" rhyme.
I kept trying to point you guys towards the number "3" because he is a 3-Star monster, has 3 eyes, and 3 toes per foot... coincidentally enough, another grouping of 3.
Take it away, Maruno.