How it works:
You step on a pressure pad and that activates the circuit which I'm not going to explain, but basically it will spawn 15 mobs at once, which you can change by looking in the dispensers. After a certain amount of time that door at the end of the hall will open and you will can continue to the healing station. The end also includes a pressure pad that deactivates the circuit and after 5 minutes the "boss fight" will be in working condition again. If you're going to use this on your own map, I do not mind, please give credit though! Also this original version is a really difficult thing to beat with almost any set of armor, I recommend either removing a couple of dispensers or putting a weaker mob into them.