alpha cutoff shader from map on map with already existing alpha channel

I am very new to shaders, and I need a very specific type of shader for creating this desired effect.

I need a shader that can be animated to do alpha cutoff from a map on a map that already have an alpha channel on its own.

Is this even possible? Or am I just being stupid here??

If for your object with this shader you don’t use light, than write shader on HLSL:

 Shader "Custom/CutoutNoLightHLSL" {
  Properties {
   _Color ("Main Color", Color) = (1,1,1,1)
   _MainTex ("Base (RGB) Trans (A)", 2D) = "white" {}
   _CutTex ("Cutout (A)", 2D) = "white" {}
   _Cutoff ("Alpha cutoff", Range(0,1)) = 0.5

  SubShader {
   Tags { "Queue" = "Transparent" }
   Pass {
    ZWrite Off // don't write to depth buffer 
    Blend SrcAlpha OneMinusSrcAlpha // use alpha blending


    #pragma vertex vert
    #pragma fragment frag

    uniform float4 _Color; // define shader property for shaders
    uniform sampler2D _MainTex;
    uniform sampler2D _CutTex;
    uniform float _Cutoff;

    struct vertexInput {
     float4 vertex : POSITION;
     float4 texcoord : TEXCOORD0;
    struct vertexOutput {
     float4 pos : SV_POSITION;
     float4 tex : TEXCOORD0;

    vertexOutput vert(vertexInput input) {
     vertexOutput output;

     output.tex = input.texcoord;
     output.pos = mul(UNITY_MATRIX_MVP, input.vertex);
     return output;

    float4 frag(vertexOutput input) : COLOR {
     float2 tp = float2(input.tex.x, input.tex.y); //get textures coordinate
     float4 col = tex2D(_MainTex, tp) * _Color; //load main texture
     float newOpacity = tex2D(_CutTex, tp).a; //load cuttext
     if(newOpacity < _Cutoff) {
      newOpacity = 0.0;
     } else { //Calculate new opacity, maybe, other formula. I don't know you parametr of change two textures
      newOpacity = col.a;
      //For example, from your pictures I see, that you change border of two textures as result. Maybe you need next calculation:
      //if (newOpacity < _Cutoff + 0.1) {
      //newOpacity = ((newOpacity - _Cutoff)/(_Cutoff + 0.1 - newOpacity)) * col.a;
      //} else {
      //newOpacity = col.a;
     return float4(col.r, col.g, col.b, newOpacity);

But, if you need object with light, write me. Than you need surface shader.I hope that it will help you.