MOSFET outputting bad waveform
I would strongly suggest you use a MOSFET driver like the MIC4416/17. Regardless of the nature of the PWM signal, whether is from a 555 timer or an MCU, a driver will level the signal up to the right Gate voltage (and buffer it for the adequate current, which for FET devices is irrelevant) to effectively turning on the transistor.

As others have pointed out, remove both capacitors from the gate and the drain, and if your load happens to be inductive, do NOT forget to add a snubber circuit and/or a flyback diode. For testing purposes, you can simply use a resistive load.