How to create destructible tile based 2D terrain like 'Broforce' does ?

Questions & Answers
1

There seems to be a particular number of bullets(damage) that each tile can take before being destroyed. There also is a blast radius of the bomb that destroys all the tiles in its’ vicinity. What aspects of Unity do I need to look into, to achieve such destructible and crumbling effects ?

3

You declare a 2-dimensional array which holds the integrity values of each block.

var world : float[,] = new float[worldSizeX, worldSizeY];

If a tile gets damages, you just decrease the float value at the coordinates.

world[2,6] -= damage;
if(world[2,6] <= 0.0f) {
     //some kind of destruction effect?
}

Getting all tiles in a radius should be easy, just use a nested loop with x - 1 to x + 1 and so on.

2

I think you should make script and attach to tiles that holds number of times you shooted at that tile. Something like:

tileLogic.js

var tileHealth : int;

function Start() {
   tileHealth = 3; 
}

function Update () {
   if(tileHealth == 0){
      Destroy (gameObject); 
   }
}

function OnCollisionEnter2D(coll: Collision2D) {
	if (coll.gameObject.tag == "Bullet")
		tileHealth--;

    if (coll.gameObject.tag == "Bullet")
		tileHealth-=3;

}

In this case you should have colliders2d on tile, bullet and bomb (size of the radius).