The effect from the ability overwrites other effects that set power and/or toughness if and only if those effects existed before the ability resolved. It will not overwrite effects that modify power or toughness (whether from a static ability, counters, or a resolved spell or ability), nor will it overwrite effects that set power and toughness which come into existence after the ability resolves. Effects that switch the creature's power and toughness are always applied after any other power or toughness changing effects, including this one, regardless of the order in which they are created.
Aven Mimeomancer
If the second ability affects a creature, it doesn't cause that creature to lose any of its abilities. It just gives that creature flying as well.
The affected creature remains 3/1 and has flying as long as it has a feather counter on it. The effect continues even if Aven Mimeomancer leaves the battlefield.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Jesper Ejsing
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
