Use [W]ASD

Here's a new simpler way to make moving platforms.

Basically the moving platform is a solid block set to not movable. Then apply velocity to the non movable object and presto, you have a platform that moves without outside force.

Why this is so useful is because the platform is acting like a "Kinematic" object. It's moving with without being affected by the physics of the world it's in. This also means you can apply X AND Y velocity that the player can ride on AND also not be affect by the player, gravity or other moving objects.

The slowing down part is an idea of mine to help someone else for their game.