Re: Dean Campbell's Christmas Bugger
I think you can go either with grizzly or medium dun. I have had about the same success with both. Maybe the slight edge goes to grizzly, but if you don't have size 20 grizzly and do have size 20 medium dun, I wouldn't run out and buy the grizzly.
If you opted to tie it as a BWO emerger, I would go with the dun.
Proper presentation and a light tippet matter more in my opinion, especially when you start talking about flies size 20 and smaller.
Best of luck to you.