Formidable!

Formidable!

Yeah, I reckoned this one would be pretty tough.

excellent!

Bravo. Needed all three minutes.

Well and truly Quimbled. Fiendish puzz.

I know it's a good grid when I feel daft for missing something.

@Wolfdog hello there..
this is absolute quality.
very tough.. & excellent.
oh how i had so many theories.... ^_^

So much fun, being a geography nerd made this the perfect mixture of fun and challenging! Excellent work!

Yep, you win.

Got then geese. Knew there were seas in there. Stuck on b group.

Tough one. Got a call in the middle so that's my excuse for not getting it :).

the flags got me

...and back to the Medums I go!

Excellent g riddling.

Nice grid! Instead of the flag colors, I linked those four as UEFA members.

Apparently just "countries" works for one of the groups

countries is all you need for the israel one lol

Really nice grid. Liked the originality of the B category a lot, and the red herrings of arctic v geese. Agree with the commenters that more than one category also worked for the flags one but a lot of fun all the same.

No arguments with the logic, but nearly impossible to get if you don't have the exact knowledge needed. More obscure than clever. I would have preferred at least one category that allowed me to use some logic or deduction rather than the whole puzzle requiring expertise in physics, chemistry, nutrition, European license plates, arctic seas, ornithology, and flag color schemes.