For FER the best strat is to go left and unlock Foxy spawns, then climb up or stay down below. Grind out cash for around 10 waves to get some good gear and try not leave behind the ammo resupply until you NEED buffs. And do NOT unlock the choking bot until you're ready to completely end your run, the damn thing will end your streak VERY fast. If you're about to be hit by foxy and you have high strength, just hold down and insta-struggle out of their grasp before they can do anything about it. It's better than taking hits and losing HP/Strength. If you're not at high strength this WILL pop hearts very fast, so don't bother unless if you're able to stave off a no hit run. The singleshot shotgun at the beginning will carry you a bit until you can unlock the gun vendi, don't sleep on its ability to pop heads.