how do i add power to an anamation like this ?

This script will work with no filtering. Here is a better link that may help explain it in more detail FilteringEnabled

Also we can use StarterCharacterScripts for tasks involving the character as we do not need to check if the character is nil. We just wait for the contents of the character.

Lastly KeyDown is deprecated, the good news is that we have a whole new service that holds all of the users input called UserInputService.

Here is an example local script which goes into the StarterCharacterScripts:-

local humanoid = script.Parent:WaitForChild('Humanoid')
local anim = Instance.new("Animation")
anim.AnimationId = "https://www.roblox.com/item.aspx?id=487738693"
local playAnim = humanoid:LoadAnimation(anim)

local usrInpServ = game:GetService('UserInputService')

-- add fire function
local function addFire()
	local torso = script.Parent:FindFirstChild('Torso') -- finds torso
	if torso then -- if torso is found
		if not torso:FindFirstChild('fire') then -- if there is no fire we add fire
			local fire  = Instance.new('Fire', torso) -- adds fire to torso
			fire.Name = 'fire'
			fire.Heat = 0
			fire.Color = Color3.new(255/255, 0, 4/255)
			fire.Size = 12
			fire.SecondaryColor = Color3.new(255/255, 0, 4/255)
		end
	end
end

usrInpServ.InputBegan:connect(function(input, gameProcessedEvent)
	if input.UserInputType == Enum.UserInputType.Keyboard then -- input must be a keyboard
		if input.KeyCode == Enum.KeyCode.Z then -- check key press 
			playAnim:Play() -- plays animation
			addFire() -- adds fire 
		end
	end
end)

To make this work with FE you would simply need to move the add fire function to the server and fire the server to add the fire to the player.

I hope this helps as it is only an example which can be built upon such as removing the fire.

Pleas comment if you do not fully understand how / why this code works but also check the wiki page first.