Thank you for the warm welcome and your help :)
Correction, I made a stupid calculation error haha. It can only generate 0.8W.
From what I did, I estimated a yoyo bearing to be 20mm wide (outer diameter) and 10mm (inner diameter) with a mass of 100g which is larger than a typical yoyo...
I want to design a yoyo that upon spinning, the energy from the spinning, can turn a mini generator inside and store that energy into a battery which then powers a LED inside.
From basic calculations, I have seen that I could probably generate about 10W of power per 'toss' due to the high rpms...