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In my Pokemon Metro Project fangame I decided to have HMs fixed to one specific Pokemon; specifically Fly and Surf. The advantage of this being the Fly/Surf sprites will be of a specific Pokemon rather than riding on a dark blue blob.
Fly will now have the same function as Surf, so instead of using it to teleport you will be able to fly from one tall building to another. Waterfall and Dive will be changed to rising higher or sinking lower in the sky. The only Pokemon to learn this new version of Fly will be "Zepblim"; a fake evolution of Drifblim. I'll also see if in Zepblim hangers you can access your Zepblim like a home base but that's just a concept for now.
For Surf you will ride on a special evolution of Lapras that can navigate the underground sewers. The evolution is called "Laplague" and evolves with a Reaper Cloth; obviously themed after Plague Doctors. Along with it's new body which is immune to the poisonous water, it has a unique battle ability called "Alchemy" that converts Poison Type attacks into medicine to heal itself.
