Pulled out a nail and a load of plaster

[KiwiKola]

Is this amount of plaster coming off the wall fixable with poly filler?

Pulled out a nail and it was almost impossible to move - ended up pulling a load of plaster with it.

Yeah of course. Just do several thin layers and sand well between them. It will be fine.

Definitely!

I like to use the quick dry polyfilla so I can get going with other layers and sanding asap and a really good and flexible filling knife. As the previous poster said it may take several thin layers. I would start by filling it so you are trying to make it flush with the surrounding plaster (do not over fill so the polyfilla is thicker than the surrounding plaster as I think it’s easier to fill with more filler later than try and sand off lots of dried filler) let that dry and then sand and fill again until smooth and level. Use fine sand paper.