The ultra proHi guys so today I will be telling you how to make a mob summoner! So first you need a large flat space of land. Next you need to get a command block and piston. This mob summoner is for waves of mobs that get harder and harder each time. First you place down a bunch of redstone wire in a straight line. Next you will need to connect a piston to the wire and put a redstone block in front of the piston. Do this ad many times as you like. Finally place a redstone wire one block ahead of the redstone block. Lastly place down multiple command blocks. In the first one type in /summon minecraft:(mob) [x] [y] [z]. In the second either type the same thing if you want more than a single mob of type in /setblock [x] [y] [z] redstone_wire. repeat as many times as you like. I hope this was helpful!
I was supposed to say "as" not "ad"