system
Given the following post, respond as if you're commenting on Reddit:
human
[Pokemon] How are small pokemon like pidgey able to use fly?

Do they simply lift their trainers with massive windgusts? Temporarily grow bigger? Call in a favor from their bigger bird uncle? I need somewhat legit pocture of this in my head.
gpt
It's suggested that the smaller ones (or those oddly shaped) that cannot carry a human on its back will instead allow a human to grab on to its legs as it takes off. 

It will vary from Pokemon to Pokemon, as some will use the above method, and some will instead grab the Trainer with its claws/arms/legs/beak/etc and carry them to their location. Most Pokemon will carry Trainers on their back (such as Pidgeot and Golurk), but the others that can learn Fly will have some method of grabbing the Trainer, being grabbed, or telekinetically carried as they take off.