There's a couple ways to obtain mob spawn eggs, but you may not want the one you have. If you combine any 2 spawn eggs with 2 items the mob is known for you'll get that mob's spawn egg instead.
For instance, to get a sheep spawn egg you'd use 2 spawn eggs with 1 wool and 1 raw mutton.
For something like a creeper spawn egg, you'd use 2 spawn eggs and 2 blast powder.
This recipe is this way so you're incentivized to value whatever the spawn egg currently is because you're trading 2 spawn eggs for 1. And you would've had to (somewhat) encountered the mob you want.
There's a couple ways to obtain mob spawn eggs, but you may not want the one you have. If you combine any 2 spawn eggs with 2 items the mob is known for you'll get that mob's spawn egg instead.
For instance, to get a sheep spawn egg you'd use 2 spawn eggs with 1 wool and 1 raw mutton. For something like a creeper spawn egg, you'd use 2 spawn eggs and 2 blast powder.
This recipe is this way so you're incentivized to value whatever the spawn egg currently is because you're trading 2 spawn eggs for 1. And you would've had to (somewhat) encountered the mob you want.