If you timed the tideswell correctly, you’ll see the on-screen text: “Elasid has unleashed the Abyssal Echo.” That’s how you know you’ve achieved the release.
While aggro players will complain that it is "cheese" and control players will call it "low skill," the numbers do not lie. The Elasid + Release the Kraken combo has the highest win rate when executed on turns 3-5 of any known deck in the format. elasid+release+the+kraken+best