Explanation:
As you can see in the picture below, this is a dihybrid cross with a twist.
We can accomplish that mutually parentages are heterozygotes for both characters because the genotypes are  
9 unicorns with curly tails (shown in green)
3 with straight tails (shown in red)
3  curly tales trait carriers with no tail (shown in dark blue)
1  straight tail trait carriers with no tail ( shown in light blue)
If this was an ordinary case of the dihybrid cross, we would get a 9:3:3:1 phenotype ratio.
However, since the first trait, the presence of the tail, is affecting the other trait, the trait texture, the ratio is altered.
 of the offspring (genotypes tt C_   and tt SS) has no tail, therefore we cannot observe the texture of the tail (some of the tailless individuals have Curly alleles -blue squares marked with green, some of them have Straight alleles -blue square marked with red ).
 of the offspring (genotypes tt C_   and tt SS) has no tail, therefore we cannot observe the texture of the tail (some of the tailless individuals have Curly alleles -blue squares marked with green, some of them have Straight alleles -blue square marked with red ).
Therefore, the altered ratio is   curly tails,
 curly tails, straight tales,
 straight tales,  tailless
 tailless