I griefed my sister's creative world by making a really big lag zone. I spawned a bunch of NPCs using dispensers and eggs. Our PC is really bad so I couldn't go close enough to kill them in any way, lava, diamond sword, or TNT. The lag zone is so bad that we couldn't use a TNT cannon.
In addition, our dad doesn't allow us to download mods so don't mention downloading single player commands and do
Please note that they are NPC villagers that are causing a lag zone.