The following mobs do not work with /spawner. Zombie, Zombie Pigman, Ghast, Slime, Magma Cube, Spider Jockey, Zombie Villager, Wither, Wither Skeleton and I'm not sure about Creeper, because I'm not sure if this server has Creeper protection (please tell me if you do). Thanks.
Mob griefing is turned off I believe. I've never seen a creeper blow up anything at my island. And as for magma cubes their command is lava slime. And slimes only spawn in certain chunks.
Ghastly have to be on a grass block to spawn and zombies are currently disabled. Not being able o spawn the other things is correct.
zombies most likely wont come back due to the fact people farm them for iron and gold which messes up the economy
It's actually the amount of grass NEEDED for gold and iron that is screwing up the economy. I had to use like 20+ grass blocks make an ANVIL which then requires Exp to use! Ridiculous!
Wither, Wither Skeleton are wayyyy to op for them to be in skyblock do you want everyone to have a beacon? or them to be worth nothing
Yes. They would still require glass, and obby to be crafted. And it takes awhile to get a head, it isn't that fast. Thing is, if this went through, it would piss off everyone who currently has a beacon.