How Do I Make Players Able To Walk Through Me?

Only way I can think of is to make a complete physics engine based off of ray casting to determine where the floor is and use body movers to move your character. That would be too much to post here tho.

Put this in a LocalScript in StarterPlayerScripts. Make sure that FilteringEnabled is on.

-- Written by Tim7775, 2015
game:GetService("RunService").Stepped:connect(function()
    for _, player in pairs(game.Players:GetPlayers()) do
        if player ~= game.Players.LocalPlayer then
            local character = player.Character
            if character then
                local head = character:FindFirstChild("Head")
                local torso = character:FindFirstChild("Torso")
                if head then head.CanCollide = false end
                if torso then torso.CanCollide = false end
            end
        end
    end
end)