Here is a real crackpot idea for this game. The background would be a skyscraper and the players window washers. A lightning strike has fused the power switch on the winch so it can't be stopped. There are a finite amount of rungs on the scaffolding. The skyscraper scrolls up one story only after all the windows on that floor are washed. The goal is to reach the ground floor before all the rungs are gone. Maybe a tolerance of 30 feet above ground and points deducted for a fall.
The main power ups to be collected are fresh pails of cleaning solution and new squeegees. Initially, a status bar would show the level and color of the solution. The color would start out as a light blue and gradually darken to brown as more dirt is cleaned. The lighter the color, the faster the windows are cleaned. Squeegee rubber gradually deteriorates and slows cleaning so they need replacing.
To make it interesting, pigeon sprites fly across the screen. If they are on course for the player then he must drop a platform or risk being knocked off. Other times the pigeons fly at greater height. Sometimes they might decide to "lighten the load" so to speak. If one of the projectiles lands in your pail the solution is instantly spoiled and must be replaced before more windows are cleaned.
There are a few details to noodle out but those are the basics. I don't seriously expect Graham H. will tackle this so late in the project but I thought I'd spring it anyway.