So you probably need some sort of “timer” in the player character or wherever you are keeping track of the players points, and once a kill is registered have that kill event call a function or something that starts the timer. Then you would need a boolean for “Kill String” so when the first kill is registered, any additional kills registered during the period where the timer is on will add to a separate variable that keeps track of the “string” of kills. once the timer ends, it will then get the value of the “string” of kills and from there you can add whatever bonus you would like to the player score depending on the number of kills registered. Then be sure to reset that number to 0 for the next time a player kills an enemy it will start the process over form 0.