There are 25 levels on each of the 3 games: Me and the Key, Me and the Key 2, and Me and the Key 3.
There are no lettered levels on Me and the Key 2.
You can add keys, but in some levels you can collect a key which unlocks an extra level.
Key levels can mean used to measure major milestones in achievement. They are used most often in education to determine when students can advance to a higher grade or advancement in a class.
Five
there are 100 levels
Four levels
4 levels
there is 25 levels + the bonus levels which there is 5 bonus levels
Find the key (see the related question below). You cannot skip levels, although you can go back to play them again. Beware because the game may reset your completion level to that earlier level!
alpha beta and omega are the three key ranks
There are 10 levels
Nine levels