After having beaten 20/20/20/20 I figure I'll give my strategy:
- Night starts, put the camera on Booty Cove immediately.
- Flick the camera up every two seconds to check on Foxy. Don't do it as fast as possible, but a quick, steady rhythm. I'd basically count: cam up, cam down, 1, 2. up, down, 1, 2, up down, 1, 2, and so on.
- If you hear footsteps, quickly tap the lights and lock the appropriate door. If Bonnie is hanging around the Cove you know it's Chica at the door, saving you a tiny bit of power. Don't let this get in the way of your rhythm.
- When Foxy leaves the Cove, drop the cameras entirely and just wait with your finger on the left door button. When you hear her charge in, slam the door in her face.
- Keep your ears out for Freddy's laugh. Once she's laughed five times (bathroom, dining room, backstage, closet, kitchen), she's in the kitchen.
- Once Freddy's in the kitchen, put the camera on the kitchen and leave it there. No exceptions - you look anywhere else, you die. Hopefully Foxy has already attacked three times by now. Your camera flicking will still slow down Foxy regardless of where you're looking, but now if she attacks you'll be trusting your reaction speed.
- Keep flicking the cameras at the same speed, but make totally sure you don't miss it once this time, as Freddy only needs a few seconds of you being out of the camera to attack.
- Foxy might attack a fourth time anyway. If you have 10%+ power this will probably end you, but if you have just a tiny bit of power it might not matter. Keep the left door ready anyway.
- Once your power has ticked over to 1%, flick the cameras a couple more times and then just don't touch anything (other than the left door if Foxy attacks), to squeeze out a few more seconds.
- Be lucky. Even with flawless execution you'll probably lose due to RNG. Simply be luckier next time.