Global variable:
var score = 0; // Player's score.
var multiply = 1.0; // Multiply rate for score.
var destCount = 0; // How many objects were destroyed just now?
Instance variable for the object:
var score = 100; // Default score if only destroyed 1 in a row.
Every tick:
multiply = destCount^2
For each object:
----If (Object was destroyed)
-------{+1 to destCount; +(object.score*multiply) to global score; destCount = 0;}
Haven't try yet but hope this would help~ ^_^