For Jacob

Butterfly.gd

extends Area2D

const FlightMagnitude = 20.0
const FlightFrequency = 5.0
const FlightSpeed = 8.0

var _current_flight_angle := 0.0
var _flying_left := 1

func _physics_process(delta : float) -> void:
    _current_flight_angle += deg2rad(FlightFrequency)
    global_position.y += FlightMagnitude * sin(_current_flight_angle) * delta
    global_position.x -= FlightSpeed * delta * (_flying_left)

Note that in my template, I change _flying_left to be equal to 1 or -1 based on whether or not it has hit a wall.