Flutter is a small butterfly found in Kirby 64: The Crystal Shards that is completely harmless and is also unable to be harmed itself. Its wings are white with black edges. Flutter simply flies around, posing no threat to Kirby. Flutter is found in Stage 1 of Planet Popstar, as well as Stage 1 of Ripple Star, which is essentially a retread of Popstar Stage 1 with different enemies, a different mid-boss battle, a different Crystal Shard location, and a different case holding a Crystal Shard itself. Flutters will fly away if Kirby gets too close.
Interestingly, Flutter has an Enemy Info Card, even though it cannot be harmed and cannot harm Kirby, unlike normal enemies.
In another title on the Nintendo 64, Super Mario 64, there are butterflies similar to Flutter that are considered enemies. Most are harmless, but a few are explosive and can harm Mario. Other times, they can help by giving Mario a 1-Up Mushroom.