The Quadropus clusters are scattered among the different levels. It's random if you will encounter one on any given level. Their effects are temporary and wear off quick, but they are relatively common so they can make quite an improvement on your play though if used right.
Yellow Quadropus Cluster: Gives bonus damage.
White Quadropus Cluster: Grants a 25% increase to running speed.
Green Quadropus Cluster: Creates bonus orbs from monster kills.
Purple Quadropus Cluster: Grants ability to steal health from enemies.
Orange Quadropus Cluster: Grants 15% increase critical hit chance.
The Quadropus Cluters are constantly changing colours, and what bonus you receive depends on the colour of the cluster when you walk over it. You can collect them right at the start of the level to get the most time from their bonus, but you may not be able to wait for the colour(and bonus) you would want the most. You could also wait until after the enemies are killed on the depth and try and time it to get the colour you want, but you will get less action with the bonus in effect this way since you will have to go down a depth to make use of the bonus.