If Guardian Idol has any +1/+1 counters on it, those counters will remain on it after it stops being a creature. Those counters will have no effect as long as Guardian Idol isn't a creature, but they will apply again if it later becomes a creature.
Activating the last ability of Guardian Idol while it's already a creature will override any effects that set its power or toughness to a specific value. Effects that modify power or toughness without setting them to a specific value will continue to apply.
A noncreature permanent that turns into a creature can attack, and its {T} abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn't matter how long the permanent has been a creature.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Igor Kieryluk
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
