extends KinematicBody2D

const ACCELERAZIONE = 500
const MAS_VELOCITA = 78.2
const FRIZIONE = 500

var velocity = Vector2.ZERO 

onready var animationPlayer = $AnimationPlayer

func _physics_process(delta):
	 var input_vector = Vector2.ZERO
	 input_vector.x = Input.get_action_strength("ui_right") - Input.get_action_strength("ui_left") 
	 input_vector.y = Input.get_action_strength("ui_down") - Input.get_action_strength("ui_up")
	 input_vector = input_vector.normalized()
	
	 if input_vector != Vector2.ZERO:
		 if input_vector.x > 0:
			 animationPlayer.play("destra")
		else:
			animationPlayer.play("sinistra")
		velocity = velocity.move_toward(input_vector * MAS_VELOCITA, ACCELERAZIONE * delta)
	else:
		animationPlayer.play("idledestra")
		velocity = velocity.move_toward(Vector2.ZERO, FRIZIONE * delta)
	
	velocity = move_and_slide(velocity)

At "else:" in the 23,1 line it says "Unindent does not match any outer indentation level". I don't know how to solve this problem.

extends KinematicBody2D

const ACCELERAZIONE = 500
const MAS_VELOCITA = 78.2
const FRIZIONE = 500

var velocity = Vector2.ZERO

onready var animationPlayer = $AnimationPlayer

func _physics_process(delta):
	var input_vector = Vector2.ZERO
	input_vector.x = Input.get_action_strength("ui_right") - Input.get_action_strength("ui_left")
	input_vector.y = Input.get_action_strength("ui_down") - Input.get_action_strength("ui_up")
	input_vector = input_vector.normalized()

	if input_vector != Vector2.ZERO:
		if input_vector.x > 0:
	         	animationPlayer.play("destra")
	    else:
			animationPlayer.play("sinistra")
			velocity = velocity.move_toward(input_vector * MAS_VELOCITA, ACCELERAZIONE * delta)
	else:
		animationPlayer.play("idledestra")
		velocity = velocity.move_toward(Vector2.ZERO, FRIZIONE * delta)
		velocity = move_and_slide(velocity)

I've fixed the code formatting in OP. Issue seems to be with lines 17, 18 and 19.

if input_vector != Vector2.ZERO:

That could be a problem. Equality/inequality tests involving floating point values may not work as expected.

Yeah, there can be floating point precision errors sometimes.

a year later