well firstly you can only have up 1 set of rocks, but as you increase the number of spikes you have on the field the more damage a pokemon will take when it comes in. There are three type of entry hazards: Stealth Rocks,Normal Spikes and Toxic Spikes. You can only set up one set of rocks, three layers of Normal Spikes and two layers of Toxic Spikes.If you have one layer of Toxic Spikes up the pokemon would get poisoned, but with two layers of Toxic Spikes the pokemon will become badly poisoned