The worlds greatest thief, Finieous Fingers was going through a dungeon corridor with his Fighter pals, and best friends of a sort, Fred and Charly. After walking for a while (and grumbling about when the DM was going to roll for wandering monsters) They saw a really strange sight. And it ran by saying loudly, "I'm late! I'm late!"
"Fred, Charly, take a look at this! A rabbit in fancy clothes and holding a pocket watch! " Finieous exclaimed, "That watch is probably worth a few hundred GP, and who knows, it might be a magic item! Let's go!"
"And think of the XP bonus!" hollered Fred as he pulled out his one handed broadsword. Charly followed suit with a +3 dagger
As they scrambled after the white rabbit, they didn't notice when the dungeon faded away, and they were running through a meadow. They eventually saw it jump into a rabbit hole and Finieous, Fred, and Charly disappeared from view as they went after it.
As they fell down they noticed a bunch of cupboards and shelves lining the walls, but when Finieous opened one, "There's nothing of value in them, just old jam jars." Eventually they hit the ground hard. and they staggered up looking like they only were spared by the fact falling damage caps at 10d6 damage.
Eventually, they followed the sound of the white rabbit to a corridor lined with doors with a single sign on the largest one which says, Wonderland Dungeon. After checking each door and rolling a check with thieves tools, the doors were all locked.
Than Fred piped up "Shouldn't we try using this tiny glass key I found on this table?"
They tried every door with it, and the one it unlocked would have not been out of place in a dollhouse. Eventually they checked where the key was and there were three bottles marked DRINK ME.
First they checked to make sure it was not a potion of poison, (good thing thieves can use magic items of any type, including identify spell scrolls,) then they each downed their potion at the same time and found themselves rapidly shrinking.
They found themselves 3 inches tall, then opened the door with the key, stepped through, and found themselves once again outside with a town in the distance, at least what they could see through the grass blades. A table with 3 more potions marked DRINK THIS, IT WILL GET YOU BACK INTO A MORE COMFORTABLE FORM.
Charly remarked, "I'm not sure if this is a good idea, the last one we drank got us in this mess." Finieous replied, "But it is the only possible solution I see, so lets drink these potions! "
They found themselves growing larger, and their forms shifting, Finieous sprouting feathers, a beak, and some wings, and morphing into a griffin, Fred and Charly polymorphing into earth ponies, and their armor and weapons adjusting.
Charly said, "I told you so."
P.S Why might they know what they are turning into? This is fantasy, don't knock it