... Again, any vanilla mob spawner can be turned into something that spawns hundreds. I remember an early Etho video where he went AFK near a dual spider spawner system he had. By the time he came back, there were a LOT -- his FPS was way down. This was when he learned to install lighting switching to turn off mob spawners.
(And frankly, if you are going to design an AFK spawner, either design in a timer to light it up after N minutes, or make sure it has an auto-killer so you don't have to try to swing a sword slowly.)
It is hard to crash a server without running it out of memory.
Slow servers can be done fairly easily, but that's different than crashing.
Servers dropping everyone's connection because a garbage collection takes too long is entirely different, and solved by using CMS -- servers should NOT use the java default throughput collector. Heck, clients should not -- travel to another dimension, watch the client do a full GC, take 15-20 seconds, and wake up already slain by something in that dimension.
