MTGNexus

A player stolen Lochmere Serpent with a Gonti, Lord of Luxury. The owner of the serpent then played Mind Flayer, gaining control of their serpent. They are arguing that if someone kills mind flayer, they would still hold control of their stolen back serpent.
Is it that true? And what happens if the effect that stole back is differently worded?

The only reason the owner has control is because the Mind Flayer's effect exists. They don't get to control it by default just because they are the owner. Once the control effect wears off, there is no longer anything giving the owner control of the Serpent.

Basically any control effect will work the same way. Most have durations or ways to end then in game while some might end based on rules. But none make the owner the default controller if they only steal it.