I was hoping that during the natural mob spawning events, we could have a hook that we could use to change the mob. The hook would pass along the entity to anything registered to receive it to a function that returned the mob after anything you wanted done to it was done.

I'm not sure how good that explanation was, so I am also going to try to explain it in code; basic code insert would be like this in SpawnerAnimals:

                                                            EntityLiving var38;

//existing code for reference
                                                            try
                                                            {
                                                                var38 = (EntityLiving)var21.entityClass.getConstructor(new Class[] {World.class}).newInstance(new Object[] {par0WorldServer});
                                                            }
                                                            catch (Exception var30)
                                                            {
                                                                var30.printStackTrace();
                                                                return var3;
                                                            }
//new code here
                                                            for (IEntitySpawnTransformer transformer : spawnTransformers)
                                                           {
                                                               var38=transformer.transform(var38,par0WorldServer,var17,var18,var19)
                                                          }
//continues with old code

This would help me with quite a few of the effects I am adding.

Thank you,

Sound Logic

Whats wrong with LivingSpecialSpawnEvent?

Well, I was hoping to transform it into another mob before the spawn check, and make it so that I could chain them properly, but I could include a chaining system seperate. I also suppose if I just kill it if a separate check doesn't work. Will LivingSpecialSpawnEvent trigger on mob spawners and such?

.... You need something a lot different. There are many places around that spawn entities. You'll need to look into and figure out where you want to really hook in.

This one is specifically for when mobs spawn naturally. And for your intentions you just need to add a new spawn type like everything else.