You have a witch's nose. Long, warty, and a 50% chance to be a disgusting green color. If you flick this nose you can create a limited version of any 1st level spell; the spell has its normal effects, but all changes made to the world are reversed after 1 hour. Magic Missile that kills someone will have them wake back up after 6 exploration turns, for example.
 Your nose becomes flat, scrunching up into your face and becoming little more then two vertical slits. You can't smell very well anymore, but your sense of taste improves. You can flick out your tongue like a snake to “taste” the air, you can sense nearby creatures by tasting their sweat or breath, and you can identify if an item is poisonous by simply flicking this tongue over the cup or meal. You can taste the tiny sweetness of the poison, mixed among the wholesome food.
 Your nose is now made of wood and looks like a stick. You sneeze leaves. You can somehow smell and breath out of the end of stick, and could use it a bit like a snorkel.
 Your nose becomes a bright red clown orb. If you squeeze it, it honks. You can cast spells on your nose which stores them for later; essentially a magical “trap” on your nose that will activate on anyone who dares squeeze it, or you could cast a useful or defensive spell on your nose to squeeze as an emergency, which doesn't have the normal speed penalties to spellcasting.
 Pig nose. +1 reaction checks to orcs and other monsters, but you look ugly and get -1 to any humans. You can smell truffles and garbage smells great to you. You also snort when you breathe sometimes and get -1 to stealth rolls.
 Your nose disappears and is replaced by a white egg with green polka-dots. The unusual coloration marks it as different from a normal egg. You can still smell from it, but can also pull it off your face whenever you wish, letting you smell things far away from your body as long as the egg is present. If the egg is ever smashed, you take 1d6 damage and can no longer smell, permanently. If you get hit by any mace or blunt attack that strikes you, you have a 1 in 4 chance for it to smash the egg as well, and falls doing damage always smashes your egg.
This egg is also slowly developing. Everything you smell is being added to the undeveloped bird embryo inside. After 4 seasons of being incubated by your face's warmth, the egg will hatch. You permanently lose your sense of smell, but a small magical avian creature identifies you as its mother. Whatever smell you smelled the most while the egg was growing determines the subtle musky scent of the bird's feathers as well as its personality. The bird can also eventually learn magic and cast 1st and 2nd level spells; squawking incantations.
 Your nose looks the same, except for the inside. Your nose's inside is extremely dry, with tough receptors and a leathery nasal cavity. You need to moisturize your nose and sinus and you can't smell anything anymore, but you totally ignore the negative effects of horrible smelling demons or undead, smell-based spells, disease-carrying miasma, and even poison gas (as long as you don't breathe through your mouth).
 Your phlegm changes in consistency. If you snort up some snot; outside of your body is hardens within a few seconds, becoming a tough cement-like substance. If you continually create mucus you can create some improvised building material, but you'll run out pretty fast.
 Your nose turns into a huge rhino horn that juts out of your face. You can use it as a 1d4 weapon by butting your head instead of doing a normal attack, and you get +1 AC, but cannot wear a mask or hide your appearance; a dark cloak over your head won't hide the protrusion.
 Pulling on your nose shows it has an elastic property. When it slaps back against your face, you take 1 damage, but gain an enhanced sense of smell; similar to a bloodhounds. You gain this sense of smell for 1d4 turns, and will need to keep pulling on your nose to continue your pursuit.