[1.7.10] spawning mobs manually in terrain gen?

[robustus]

Maybe someone can help me I was looking for more control over the spawning of my custom mobs, for example wanted to make a very very rare mob but it seem the normal way to do it even if you put very low weight on how many mobs spawn its still much more than I want, I was wondering if anyone knows of a code to spawn a single mob like you would a regular block during terrain gen, like how setblock would do it for blocks, is there a way to do with this mobs?

 

Thanks