I have no clue why this is not working it should be working fine?
local Players = game:GetService("Players")
local Character = PlayerAdded:WaitForChild("Character")
Character.Humanoid.JumpPower = 35
Character isn’t a child, it’s a property. Rather than using WaitForChild, use the Wait function of events:
local Character = PlayerAdded.Character or PlayerAdded.Character:Wait()
This will wait for the character to load if it doesn’t exist yet. This will only work once though, you probably want to use CharacterAdded straight up
character.Humanoid.JumpPower = 35