So, this is something I wish would happen a lot more in the Mario series than it actually does. Bowser actually gets to use his nose for once. I swear, it's like people are allergic to having him sniff. The only animation I've ever seen involving Bowser sniffing (and it not being gross) is Seth The Wolf's unlisted videos of him sneezing from what's going into his nose, be it Fire Flower pollen or black pepper (the latter you can find on this site if you look up his user page). In the games proper, he only sniff a grand total of 4 times, 3 in Bowser's Inside Story and 1 in Dream Team, none of which are very close to him or his nose, and none of which have his sniffing be audible and instead make it mute.

Well, I'm unable to fix the "inaudible sniffing" problem since I don't have any kind of recording set up, but at least I can fix the "no good look at Bowser's sniffing nose" one.

As for what he smells, it's basically a subspecies of that one flower from Bowser's Inside Story that caused a mini-game in his nose where Mario and Luigi had to use the pollen to make him sneeze. Except in this case, there's no Fawful, no brotherly italian plumbers in Bowser's system and this subspecies not only has pollen that's perfectly able to go into any sinus without causing any kind of irritation, but the flower smells even better than the ones he sniffed in BIS. As such, Bowser is completely free to sniff the scent to his heart's content.

Also, fun fact: I made this art in pixels like most of my art thus far (barring the first two submissions), but this is the first one to be 1000 pixels in either height or diameter, let alone both.