Let’s assume that dragons show incomplete dominance for fire breathing. the f allele provides lots of fire and the f’ allele gives no fire.

if a dragon that has very strong fire is crossed with a dragon that has a moderate fire, what will their offspring be like?

The progenies of the dragons with strong fire and dragon with no fire will be dragons with fire at medium rate.

Incomplete dominance is the phenomenon when two different alleles are present in a same organism gives a mixed type of phenotype which isn't similar to any characters of the parents.

In case of the dragons, the genotype of the dragons with strong fire = FF.

The genotype of the dragons with no fire = F'F'.

So the gametes produced by the dragon with strong fire is F and that by the dragons with no fire is F'.

So the dragons produced as a progeny = FF'.

As this gene shows incomplete dominance, so both the characters will be mixed and present as a mixed character. So the offsprings will be moderately fire breathing.