Get an auto-spawner with MFR, capture a wither skeleton with a Re-usable safari net. Get a steam turbine to power the auto-spawner and place in the skeleton re-usable safari net and change to make exact copies. It also requires mob essence, you can get this by making an XP extractor, extracting 1 level which then produces 1 bucket; 1000MB, the auto spawner can only hold a maximum of only 4000MB, so that means 4 levels/buckets. Now after you have them spawning, you'll actually want a grinder set up which can completely annihilate any mobs in a 5x5 radius. So just make a 5x5 room that contains an auto-spawner and a grinder. A grinder requires RF to run, so stick another steam turbine beside it to run it. The grinder produces Mob essence when it grinds mobs, which can then be fed back into the auto spawner for more mobs! Although I believe that it only produces 1/4 of a bucket of mob essence (250MB). The grinder should also be hooked up to a chest, the grinder does in-fact collect wither skeletons. I have over 3 stacks myself! And if you think the spawner is not spawning enough... You can head over to the config and change the amount of work the auto-spawner requires, therefore it will create lots more mobs! Best of luck!
I don't want to use turtles and I don't really wanna use mffs but can if