Why are changes to the morph visible only to the client?

You today are going to learn to use RemoteEvents~

Okay, so for starters, it's only on the client side because it's a LOCAL script, meaning it'll only happen locally. To make it Server-side you'll have to make a Serverscript that catches the event. It's a little more code but worth it in the end. :P

-- Note: Put this script inside the ScreenGui, not the Buttons themselves.
-- ClientSideScript

-- || Services ||
local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

-- || Variables ||
local AnimationRemote = ReplicatedStorage:WaitForChild("AnimationRemote")
local Player = Players.LocalPlayer
local Character = Player.Character or Player.CharacterAdded:wait()
local SmileButton -- = ButtonPathHere
local FrownButton -- = ButtonPathHere

-- || EventTriggerer ||
SmileButton.MouseButton1Click:connect(function()
AnimationRemote:FireServer("Smile")
end)

FrownButton.MouseButton1Click:connect(function()
AnimationRemote:FireServer("Frown")
end)

So, we've just set up to make it so the Buttons trigger something called a RemoteEvent, now we just have to create that RemoteEvent so it doesn't error.

-- Note: Put this script inside of ServerScriptService
-- ServerSideScript

-- || Services ||
local ReplicatedStorage = game:GetService("ReplicatedStorage")

-- || Variables ||
local AnimationRemote = Instance.new("RemoteEvent", ReplicatedStorage) AnimationRemote.Name = "AnimationRemote"

-- || EventHandler ||
AnimationRemote.OnServerEvent:connect(function(Ply, Animation)
if Animation == "Smile" then
Ply.Character.Chest:FindFirstChild("Smile").Transparency = 0
Ply.Character.Chest:FindFirstChild("Frown").Transparency = 1
elseif Animation == "Frown" then
Ply.Character.Chest.FindFirstChild("Smile").Transparency = 1
Ply.Character.Chest:FindFirstChild("Frown").Transparency = 0
end
end)

Be sure to let me know if I missed something

So far, I've made the Client fire the event to the server, which makes the Player's Animation changed based on the button pressed!

If this doesn't work, let me know in a comment and I'll edit the code.

Filtering Enabled

RemoteEvents/RemoteFunctions

Best of luck!