We've had some fun moments in the campaign that I've run.  I'd need access to one of my player's notes to really post up (he has a list of the best quotes from sessions).

Buuuut...

Probably some of the most fun came from what I chose to use as a 'first boss', letting the players (and to a lesser extent myself) figure out the game.

Basically, I created mogwai - as in, classic Gremlins movie style, don't feed after midnight, don't get wet, mogwai (with liberties taken - for instance, they need to deliberately choose to breed instead of it happening automatically).  Their leader was powerful enough to use a glamour and ran a Chinese restaurant with... dubious ingredients.

At that time, we had two apprentice wizards, a were-ox, and one I can't remember what he was playing.  They ended up getting into a fight with the mogwai in the forest, which could've been bad for them... except (with no 'fudging' from me) the mogwai were constantly, consistently failing miserably at everything they did.  With fireworks and traps and everything.  Which worked perfectly, because epic fail is kinda what gremlins do best, even when it's happening to them.  Eventually they defeated them, and then eventually their boss as well, but it didn't end there, somewhat to my surprise.

They ended up... well, not exactly adopting, but took in one of the mogwai.  They ended up calling him Mog, since when they asked him what his name was he said "Mog... wai?"  Effectively, one of the apprentices ended up taking him in, and he lived in the fridge.  It was something of an ongoing joke for quite awhile, because every so often he'd pipe in from the fridge and they'd shut him up with a corndog.  And he kept getting bigger, and bigger...

Later on in the campaign, a black court vampire attacked the house - they didn't think Mog was safe, so they told him take all the corndogs and run down to the river.

... yes, they told a mogwai to run outside at night, to water, with a bunch of food.

Soooo they dealt with the black court vampire, and then the vampire's master... only to soon after hear about strange sightings and disturbances down by the river.  Sighing, they geared up, and went to investigate... to find Mog holding a rave in a run-down old shack, MUCH bigger, very urbane (think Brain-Gremlin from Gremlins 2), with a bunch of smaller mogwai following after him.  After a bit of talking, they find out that the ones causing the disturbance is a splinter group that broke off from Mog's 'tribe'.

They investigate (it's winter at this point, by the way), and they end up confronting Wai - the leader of the splinter sect.  It turned out that the main reason that they split off from Mog's tribe was that they don't like corndogs - HERESY!  Only problem was, instead they were hunting livestock and the occasional pet - given time, it might have even escalated further.  The group challenged the tribe to a fight, but they didn't want to hurt them, and the mogwai tribe was more in the mood for mischief and fun anyway...

Cue epic snowball fight that lasted the last half of the session - the kind that can only occur when one of the (by now) wizards in the party is a water mage.  Who, of course, won in the end, getting Wai with a huge snowball and taking him out.

After the more serious arc prior with the master black vampire, the players all appreciated the breather, and had a lot of fun with the session.  Much laughter and shenanigans were had, they got some solid roleplay in, and they had a combat where no one actually got hurt.

Fun times.