entityregistering.java

((Map) getPrivateStatic(EntityTypes.class, "c")).put(paramString, paramClass);
    //Registers the name to the mob, this appears to be for saving nbt tags.  Theoretically, this will turn all mobs in your world into your mob, so maybe you shouldn't touch it.
((Map) getPrivateStatic(EntityTypes.class, "d")).put(paramClass, paramString);
    //Registers the name you provided.  This appears to be used by stuff and not do anything wrong, so you should probably leave this one.
((Map) getPrivateStatic(EntityTypes.class, "e")).put(Integer.valueOf(paramInt), paramClass);
    //Registers mob id to this mob, which, I believe, will cause it to become the default mob class for the id provided.
((Map) getPrivateStatic(EntityTypes.class, "f")).put(paramClass, paramInt);
    //Registers the mob to the mob id.  This is essentially the reverse of e, and, I believe, assigns how the mob will display to clients.  I'm pretty sure the client crashes without this one.
((Map) getPrivateStatic(EntityTypes.class, "g")).put(paramString, Integer.valueOf(paramInt));
    //This registers the name provided to the id, not sure what this is for, it doesn't appear to be used by anything.