You were invited here because you are using Nukes/Napalm/Reflect Damage/etc against the boss levels in the Steam Summer Sale Mini Game.

The boss levels are every 10 levels where the level number ends in 0.
You will see a Crown Icon in the Lane with the Boss.
This is where you want to deploy Raining Gold and Treasure.

DO NOT USE SPECIAL ATTACKS AGAINST THE BOSS
Because then you waste all the Gold Multipliers that other people are using.

Just click the boss like crazy and count your money when they finally die.

Get it?