Check out this example
https://howtoconstructdemos.com/create-a-reflection-with-water-effect/
Thanks, dude. :)
This is a great solution for a mirror, not a river or sea, as it is a large routine focused on just one object (the player character, for example).
I actually got what I wanted, but I would like to not have the flicking in the reflection. :/
By the way, I'm using Construct 2.