Unity 2D jump through platforms with fall support.

JumpThrough.cs

using UnityEngine;
using System.Collections;

public class Platform : MonoBehaviour {
	SpriteRenderer playerGraphic;
	Rigidbody2D playerBody;
	BoxCollider2D playerBox;
	CircleCollider2D playerCircle;
	
	float padTop = -0.2f; // Padding applied to the top of feet platform checks (prevents player from barely standing on platform)
	bool visible; // Is the player able to interact with the platform
	
	[SerializeField] bool enableDrop;

	void Start () {
		GameObject player = PlayerAPI.current.gameObject;
		playerGraphic = player.GetComponent<SpriteRenderer>();
		playerBody = player.GetComponent<Rigidbody2D>();
		playerBox = player.GetComponent<BoxCollider2D>();
		playerCircle = player.GetComponent<CircleCollider2D>();
		
		ToggleCollision(playerGraphic.bounds.min.y > collider2D.bounds.max.y + padTop, playerBody.velocity.y, true);
	}
	
	void FixedUpdate () {
		if (!IsDropping()) {
			ToggleCollision(playerGraphic.bounds.min.y > collider2D.bounds.max.y + padTop, playerBody.velocity.y);
		} else {
			ToggleCollision(false);
		}
	}
	
	bool IsDropping () {
		if (!enableDrop) return false;
		return Input.GetAxis("Vertical") < -0.01f && Input.GetButton("Jump");
	}
	
	void ToggleCollision (bool isEnabled) {
		// Fake a submission to get the values toggled
		if (isEnabled) {
			ToggleCollision(true, -5f);
		} else {
			ToggleCollision(false, 0f);
		}
	}
	
	void ToggleCollision (bool above, float velY, bool force = false) {
		if (above == visible && !force) return;
		
		// Check if falling and and above the platform
		if (above && velY < 0.1f) {
			ToggleColliders(false);
			SetDepth(0f);
			visible = true;
		} else {
			ToggleColliders(true);
			SetDepth(-5f);
			visible = false;
		}
	}
	
	void ToggleColliders (bool ignore) {
		Physics2D.IgnoreCollision(collider2D, playerBox, ignore);
		Physics2D.IgnoreCollision(collider2D, playerCircle, ignore);
	}

	// With setting the depth you can prevent ground checks from firing false positives
	void SetDepth (float depth) {
		Vector3 pos = transform.position;
		pos.z = depth;
		transform.position = pos;
		
	}
}