Almost all online slots have bonus games on the second screen. They’re usually based on luck (for example selecting numbers or matching symbols), but players don’t mind it because so are the main slots. There are some bonus games that require skills, though. It’s either mechanical dexterity or logical reasoning.
The first skill is required in games such as Asteroid Blasteroid in the Cosmic Quest Episode One i-slot game by Rival Gaming. You steer a spaceship and avoid being hit by asteroids (you lose a bit of your life if you get hit), while firing at them to destroy them. The game is over either when you lose the entire life or when all asteroid are destroyed. For the latter you get rewarded with bonus credits. Another game requiring dexterity is the bonus game of Hole in Won, based on golf, where you need to aim well and hit the ball the right way.
Logical reasoning is required in games like Battleships, which inspired a casino called Battleship Search and Destroy created by WagerWorks. The bonus game is called Sink the Fleet and it’s a one-player version of Battleships. 17 squares on an 8×8 grid are generated at random. You need to find all the ships of the enemy fleet using feedback from your previous moves regarding hits and misses. You can’t lose more than 8 times. Successful hits mean bonus credits. If you don’t want to play this strategic game, you can choose a luck based bonus game instead.