Part 4 complete code

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PolygonGenerator.cs: Generates the terrain, placed on a gameobject with a mesh filter, a mesh renderer, a mesh collider and the tilesheet as the material.

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class PolygonGenerator : MonoBehaviour {
 
 public List<Vector3> newVertices = new List<Vector3>();
    public List<int> newTriangles = new List<int>();
  public List<Vector2> newUV = new List<Vector2>();
 
 public List<Vector3> colVertices = new List<Vector3>();
    public List<int> colTriangles = new List<int>();
 private int colCount;
 
 private Mesh mesh;
 private MeshCollider col;
 
 private float tUnit = 0.25f;
 private Vector2 tStone = new Vector2 (1, 0);
 private Vector2 tGrass = new Vector2 (0, 1);
 
 
 public byte[,] blocks;
 private int squareCount;
 public bool update=false;
 
 
 // Use this for initialization
 void Start () {
  mesh = GetComponent<MeshFilter> ().mesh;
  col = GetComponent<MeshCollider> ();
  
  GenTerrain();
  BuildMesh();
  UpdateMesh();
 }
 
 void Update(){
  if(update){
   BuildMesh();
   UpdateMesh();
   update=false;
  }
 }
 
 
 int NoiseInt (int x, int y, float scale, float mag, float exp){
 
  return (int) (Mathf.Pow ((Mathf.PerlinNoise(x/scale,y/scale)*mag),(exp) ));
  
  
 }
 
 void GenTerrain(){
  blocks=new byte[96,128];
  
  for(int px=0;px<blocks.GetLength(0);px++){
   int stone= NoiseInt(px,0, 80,15,1);
   stone+= NoiseInt(px,0, 50,30,1);
   stone+= NoiseInt(px,0, 10,10,1);
   stone+=75;
   
   
   int dirt = NoiseInt(px,0, 100f,35,1);
   dirt+= NoiseInt(px,100, 50,30,1);
   dirt+=75;
   
   
   for(int py=0;py<blocks.GetLength(1);py++){
    if(py<stone){
     blocks[px, py]=1;
     
     if(NoiseInt(px,py,12,16,1)>10){  //dirt spots
      blocks[px,py]=2;
      
     }
     
     if(NoiseInt(px,py*2,16,14,1)>10){ //Caves
      blocks[px,py]=0;
      
     }
     
    } else if(py<dirt) {
     blocks[px,py]=2;
    }
    
    
   }
  }
 }
 
 void BuildMesh(){
  for(int px=0;px<blocks.GetLength(0);px++){
   for(int py=0;py<blocks.GetLength(1);py++){
    
    if(blocks[px,py]!=0){
     
    GenCollider(px,py);
     
     if(blocks[px,py]==1){
      GenSquare(px,py,tStone);
     } else if(blocks[px,py]==2){
      GenSquare(px,py,tGrass);
     }
    }
   }
  }
 }
 
 byte Block (int x, int y){
  
  if(x==-1 || x==blocks.GetLength(0) || y==-1 || y==blocks.GetLength(1)){
   return (byte)1;
  }
  
  return blocks[x,y];
 }
 
 void GenCollider(int x, int y){
  
  
  //Top
  if(Block(x,y+1)==0){
  colVertices.Add( new Vector3 (x  ,  y  , 1));
  colVertices.Add( new Vector3 (x + 1 ,  y  , 1));
  colVertices.Add( new Vector3 (x + 1 ,  y , 0 ));
  colVertices.Add( new Vector3 (x  ,  y  , 0 ));
  
  ColliderTriangles();
  
  colCount++;
  }
  
  //bot
  if(Block(x,y-1)==0){
  colVertices.Add( new Vector3 (x  ,  y -1 , 0));
  colVertices.Add( new Vector3 (x + 1 ,  y -1 , 0));
  colVertices.Add( new Vector3 (x + 1 ,  y -1 , 1 ));
  colVertices.Add( new Vector3 (x  ,  y -1 , 1 ));
  
  ColliderTriangles();
  colCount++;
  }
  
  //left
  if(Block(x-1,y)==0){
  colVertices.Add( new Vector3 (x  ,  y -1 , 1));
  colVertices.Add( new Vector3 (x  ,  y  , 1));
  colVertices.Add( new Vector3 (x  ,  y  , 0 ));
  colVertices.Add( new Vector3 (x  ,  y -1 , 0 ));
  
  ColliderTriangles();
  
  colCount++;
  }
  
  //right
  if(Block(x+1,y)==0){
  colVertices.Add( new Vector3 (x +1 ,  y  , 1));
  colVertices.Add( new Vector3 (x +1 ,  y -1 , 1));
  colVertices.Add( new Vector3 (x +1 ,  y -1 , 0 ));
  colVertices.Add( new Vector3 (x +1 ,  y  , 0 ));
  
  ColliderTriangles();
  
  colCount++;
  }
  
 }
 
 void ColliderTriangles(){
  colTriangles.Add(colCount*4);
  colTriangles.Add((colCount*4)+1);
  colTriangles.Add((colCount*4)+3);
  colTriangles.Add((colCount*4)+1);
  colTriangles.Add((colCount*4)+2);
  colTriangles.Add((colCount*4)+3);
 }
 
 
 void GenSquare(int x, int y, Vector2 texture){
  
  newVertices.Add( new Vector3 (x  ,  y  , 0 ));
  newVertices.Add( new Vector3 (x + 1 ,  y  , 0 ));
  newVertices.Add( new Vector3 (x + 1 ,  y-1 , 0 ));
  newVertices.Add( new Vector3 (x  ,  y-1 , 0 ));
  
  newTriangles.Add(squareCount*4);
  newTriangles.Add((squareCount*4)+1);
  newTriangles.Add((squareCount*4)+3);
  newTriangles.Add((squareCount*4)+1);
  newTriangles.Add((squareCount*4)+2);
  newTriangles.Add((squareCount*4)+3);
  
  newUV.Add(new Vector2 (tUnit * texture.x, tUnit * texture.y + tUnit));
  newUV.Add(new Vector2 (tUnit * texture.x + tUnit, tUnit * texture.y + tUnit));
  newUV.Add(new Vector2 (tUnit * texture.x + tUnit, tUnit * texture.y));
  newUV.Add(new Vector2 (tUnit * texture.x, tUnit * texture.y));
  
  squareCount++;
  
 }
 
 void UpdateMesh () {
  mesh.Clear ();
  mesh.vertices = newVertices.ToArray();
  mesh.triangles = newTriangles.ToArray();
  mesh.uv = newUV.ToArray();
  mesh.Optimize ();
  mesh.RecalculateNormals ();
  
  newVertices.Clear();
  newTriangles.Clear();
  newUV.Clear();
  squareCount=0;
  
  Mesh newMesh = new Mesh();
  newMesh.vertices = colVertices.ToArray();
  newMesh.triangles = colTriangles.ToArray();
  col.sharedMesh= newMesh;
  
  colVertices.Clear();
  colTriangles.Clear();
  colCount=0;
 }
}

ColliderExample: Placed on a gameobject, destroys blocks in an area around itself.

using UnityEngine;
using System.Collections;

public class ColliderExample : MonoBehaviour {
 
 public GameObject terrain;
 private PolygonGenerator tScript;
 public int size=4;
 public bool circular=false;
 // Use this for initialization
 void Start () {
 
  tScript=terrain.GetComponent(\"PolygonGenerator\") as PolygonGenerator;
  
 }
 
 // Update is called once per frame
 void Update () {
 
  
  bool collision=false;
  for(int x=0;x<size;x++){
   for(int y=0;y<size;y++){
    if(circular){
     
     if(Vector2.Distance(new Vector2(x-(size/2),y-(size/2)),Vector2.zero)<=(size/3)){
     
      if(RemoveBlock(x-(size/2),y-(size/2))){
      
       collision=true;
      }
      
     }
    } else {
      
     if(RemoveBlock(x-(size/2),y-(size/2))){
      
      collision=true;
     }
    }
    
   }
  }
  if( collision){
   tScript.update=true;
   
  }
   
   
   
 }
 
 
 bool RemoveBlock(float offsetX, float offsetY){
  int x =Mathf.RoundToInt(transform.position.x+offsetX);
  int y=Mathf.RoundToInt(transform.position.y+1f+offsetY);
  
  if(x<tScript.blocks.GetLength(0) && y<tScript.blocks.GetLength(1) && x>=0 && y>=0){
  
   if(tScript.blocks[x,y]!=0){
    tScript.blocks[x,y]=0;
    return true;
   }
  }
  return false;
 }
 
}

RaycastExample: GameObject shoots ray towards a target gameobject and creates a block on every face it hits or destroys every block it hits.

using UnityEngine;
using System.Collections;

public class RaycastExample : MonoBehaviour {
 
 public GameObject terrain;
 private PolygonGenerator tScript;
 public GameObject target;
 private LayerMask layerMask = (1 << 0);
 
 // Use this for initialization
 void Start () {
 
  tScript=terrain.GetComponent(\"PolygonGenerator\") as PolygonGenerator;
  
 }
 
 // Update is called once per frame
 void Update () {
 
  
   
  RaycastHit hit;
  
  float distance=Vector3.Distance(transform.position,target.transform.position);
  
  if( Physics.Raycast(transform.position, (target.transform.position - transform.position).normalized, out hit, distance , layerMask)){
   
   Debug.DrawLine(transform.position,hit.point,Color.red);
   
   Vector2 point= new Vector2(hit.point.x, hit.point.y);
   point+=(new Vector2(hit.normal.x,hit.normal.y))*0.5f;
   
   Debug.DrawLine(hit.point,new Vector3(point.x,point.y,hit.point.z),Color.magenta);
   
   tScript.blocks[Mathf.RoundToInt(point.x-.5f),Mathf.RoundToInt(point.y+.5f)]=1;
   tScript.update=true;
   
  } else {
   Debug.DrawLine(transform.position,target.transform.position,Color.blue);
  }
 }
}