How do I make a Animation Trigger?

I want to make a Animation Trigger for a horror game. So when Player steps on a part, a NPC will do an animation.

Can anyone help me?

In the same way you use :LoadAnimation() on a player's humanoid, you'd use it on an NPC's humanoid inside a touch event. So once touched, use :LoadAnimation() on the NPC and then just :Play() it.

Here is something that will help you. Replace the animationID variable with your own animation id.

local part = script.Parent
local NPC = game.Workspace.NPC
local animationID = 1338744180

part.Touched:connect(function(hit)
	if hit.Parent:FindFirstChild("Humanoid") ~= nil then --checks if hit is a player
		local Animation = Instance.new("Animation",NPC)
		Animation.AnimationId = "http://www.roblox.com/Asset?ID="..animationID
		local LoadedAnimation = NPC.Humanoid:LoadAnimation(Animation)
		LoadedAnimation:Play()
	end
end)

Enjoy and thanks for posting.