Below is a Punnett square showing the gametes that will be formed by a blue monster (BB) and a green monster (bb):
B B
b Bb Bb
b Bb Bb
So, based on the above, the:
Parent 1: B B
Parent 2: b b
Gametes: B B
Offspring: BB Bb
Since the blue monster is homozygous for the blue trait (BB), it will produce only one type of gamete, which is B. Likewise, since the green monster is homozygous for the green trait (bb), it will produce only one type of gamete, which is b.
When these gametes are combined, we get a 1:1:1:1 ratio of offspring with the blue trait (BB), the hybrid trait (Bb), the green trait (Bb), and the green trait (bb), respectively.
This is in accordance with the law of segregation, which states that each parent contributes one of its two alleles to each offspring, and that these alleles segregate from each other during gamete formation.