If an activated or triggered ability of a permanent that isn’t a delayed triggered ability of that permanent tries to convert it, the permanent does so only if it hasn’t converted or transformed since the ability was put onto the stack. If a delayed triggered ability of a permanent tries to convert that permanent, the permanent does so only if it hasn’t converted or transformed since that delayed triggered ability was created. In both cases, if the permanent has already transformed or converted, an instruction to do either is ignored.
November 18, 2022 · The Brothers’ War
Some triggered abilities trigger when an object “transforms into” an object with a specified characteristic. Such an ability triggers if the object either transforms or converts (see rule 701.50) and has the specified characteristic immediately after it does so.
July 3, 2020 · Core Set 2021
Some triggered abilities trigger when an object “transforms into” an object with a specified characteristic. Such an ability triggers if the object transforms and has the specified characteristic immediately after it transforms.