Unity Sprite Shadow and Flashable Shader

sprite.shader

// Combination of https://pastebin.com/yRPktdSP (https://www.youtube.com/watch?v=flu2PNRUAso) and https://gist.github.com/ilhamhe/81b285fd302d7964d18c22ad05857343

Shader "Sprites/Custom/Sprite"
{
	Properties
	{
		[PerRendererData] _MainTex ("Sprite Texture", 2D) = "white" {}
		_Color ("Tint", Color) = (1,1,1,1)
		[MaterialToggle] PixelSnap ("Pixel snap", Float) = 0
		_FlashColor ("Flash Color", Color) = (1,1,1,1)
		_FlashAmount ("Flash Amount", Range (0,1)) = 0
        _Cutoff("Alpha Cutoff", Range(0,1)) = 0.5
	}

	SubShader
	{
		Tags
		{ 
			"Queue"="Transparent" 
			"IgnoreProjector"="True" 
			"RenderType"="Transparent" 
			"PreviewType"="Plane"
			"CanUseSpriteAtlas"="True"
		}

		Cull Off
		Lighting Off
		ZWrite Off
		Blend One OneMinusSrcAlpha

		Pass
		{
		CGPROGRAM
			#pragma vertex vert
			#pragma fragment frag
			#pragma multi_compile _ PIXELSNAP_ON
			#include "UnityCG.cginc"
			
			struct appdata_t
			{
				float4 vertex   : POSITION;
				float4 color    : COLOR;
				float2 texcoord : TEXCOORD0;
			};

			struct v2f
			{
				float4 vertex   : SV_POSITION;
				fixed4 color    : COLOR;
				float2 texcoord  : TEXCOORD0;
			};
			
			fixed4 _Color;
			fixed4 _FlashColor;

			v2f vert(appdata_t IN)
			{
				v2f OUT;
				OUT.vertex = UnityObjectToClipPos(IN.vertex);
				OUT.texcoord = IN.texcoord;
				OUT.color = IN.color * _Color;
				#ifdef PIXELSNAP_ON
				OUT.vertex = UnityPixelSnap (OUT.vertex);
				#endif

				return OUT;
			}

			sampler2D _MainTex;
			sampler2D _AlphaTex;
			float _AlphaSplitEnabled;
			float _FlashAmount;


			fixed4 SampleSpriteTexture (float2 uv)
			{
				fixed4 color = tex2D (_MainTex, uv);

				if (_AlphaSplitEnabled) 
					color.a = tex2D (_AlphaTex, uv).r;

				return color;
			}

			fixed4 frag(v2f IN) : SV_Target
			{
				fixed4 c = SampleSpriteTexture (IN.texcoord) * IN.color;
				c.rgb = lerp(c.rgb, _FlashColor.rgb, _FlashAmount);
				c.rgb *= c.a;
				return c;
			}
			ENDCG
		}
	}
	SubShader
    {
        Tags
    {
        "Queue" = "Transparent"
        "IgnoreProjector" = "True"
        "RenderType" = "Transparent"
        "PreviewType" = "Plane"
        "CanUseSpriteAtlas" = "True"
    }

        Cull Off
        Lighting Off
        ZWrite Off
        Blend One OneMinusSrcAlpha

        CGPROGRAM
        #pragma surface surf Lambert vertex:vert alphatest:_Cutoff addshadow nofog nolightmap nodynlightmap keepalpha noinstancing
        #pragma multi_compile_local _ PIXELSNAP_ON
        #pragma multi_compile _ ETC1_EXTERNAL_ALPHA
        #include "UnitySprites.cginc"

        struct Input
        {
            float2 uv_MainTex;
            fixed4 color;
        };

        void vert(inout appdata_full v, out Input o)
        {
            v.vertex = UnityFlipSprite(v.vertex, _Flip);

            #if defined(PIXELSNAP_ON)
            v.vertex = UnityPixelSnap(v.vertex);
            #endif

            UNITY_INITIALIZE_OUTPUT(Input, o);
            o.color = v.color * _Color * _RendererColor;
        }

        void surf(Input IN, inout SurfaceOutput o)
        {
            fixed4 c = SampleSpriteTexture(IN.uv_MainTex) * IN.color;
            o.Albedo = c.rgb * c.a;
            o.Alpha = c.a;
        }
        ENDCG
	}
}