How common games can increase to fast?

As games like Ironpants, clumsy bird can increase so fast? What kind of promoting these games made​​?
which the best way?

Those games are very popular because they are recreations of the popular game Flappy Bird which was a strange huge success. Flappy Bird was removed from Google Play by its creator so other similar games (like the ones you mentioned) picked up the trend.

Yes this is true. But for these game go to the top they need promotion. Because everybody was looking for Flappy Bird and not for Ironpants or Clusmy Bird.
I read a thread from the Ironpants creator, and he said the game was getting just 5 downloads per day in the begin .

Clumsy Bird ranked #1 in the US for the keywords “flappy bird” after the original was gone and in the Top 5 results before.
This pushed it to #1 Free New App and later to #1 Free App.