My Remote Event won't work properly???

The first parameter of OnClientEvent is not the player, as you can just get the player through game.Players.LocalPlayer in a LocalScript. However, when you fire a remote event to the server, the server doesn't know which player has fired it, so the first argument of OnServerEvent will be the player in that case. So, all you should have to do is remove the Plr as an argument, and just use the player variable from above to refer to the LoclPlayer. Also, PlayerGui is with a capital P, and capitalisation matters in Lua. If you are not referring to the PlayerGui through the player, you can use your lowercase p playerGui variable from above.

For example:

local debounce = false

local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local player = Players.LocalPlayer
local GuiClicker = ReplicatedStorage:WaitForChild("GuiClicker")
local playerGui = player:WaitForChild("PlayerGui")


local function OnGuiClickerFired()
    if debounce == false then

        playerGui.InfoPanel.ScrollingFrame:TweenPosition(UDim2.new(0.5, -250,0.5, -200, 'Out', 'Bounce', 1))
        debounce = true
    else
        playerGui.InfoPanel.ScrollingFrame:TweenPosition(UDim2.new(-0.5, -250,0.5, -200, 'Out', 'Bounce', 1))
        playerGui.InfoPanel.ScrollingFrame.Visible = true
        debounce = false
    end
end

GuiClicker.OnClientEvent:Connect(OnGuiClickerFired)

You might also want to check if you are setting Visible to true in the right section.