By the 'game over' screen you mean this?
Well, you'll only reach it if you lose all your Health (as in reach 0) without the No Fail mod on.
Other conditions that also triggers it are:
- Hardcore mod - Your health instantly drops to 0 if you miss a beat or break the combo.
- "Pretty much every other mode" - When your health depletes away to 0.^
^ Note that the Perfect (SS or Quit) mod restarts (same as pressing Ctrl-R) the beatmap when you mess up the perfect run (100, miss or combo break).
As for avoiding this, refer to this osu! Wiki quote
- The top left bar is your "health".
- This will decrease at a steady rate, depending on the beatmap difficulty set by the mapper(s), but you can replenish it by hitting notes at the right time.
- A perfectly timed hit (300 hit or Geki Beat) will increase your health more than a badly timed hit (50 hit).
- A total miss will take a good chunk out of your health.
Depending on the difficulty of the beatmap, your perfect (or on-time beats) and misses will affect your score differently.
The drain rate determines the speed your health depletes.
The higher the drain rate, the more accurate you'll have to be to avoid draining faster than your hits can return.
Just to be clear, a 50, 100, 300 will increase your health, while misses, combo breaks will take a chunk out of your health.
Apart from that, messing up (missing) a beat or breaking a combo will remove 1/4-1/3# of your health bar.
# It's either 1-third or 1-quarter.
Note: Combos are broken when your combo count (bottom left) is reset to 0.
This happens when you:
- Miss a beat (also counts as a Miss)
- Didn't turn a spinner fast enough (also counts as a Miss)
- Release the key on a slider too early (also counts as a 100)
- Missed the start of a slider but still manage to catch up and drag (also counts as a 100)
- Missed a slider completely; not click/dragged at all (also counts as a Miss)
Your combo is basically a score multiplier and can be increased by:
- Hitting a note on time (scoring a 50, 100 or 300)
- Spinning a Spinner in time
- Starting a slider
- Staying on a slider (without breaking the combo) whilst going over a beat.
- Staying on a slider, hitting the reverse.
- Completing a slider.
(Which is why sliders can create ridiculous combos whilst scoring very little)
In Osu!, pp stands for performance points. There are two main contexts to consider pp in, at the beatmap level and at the account level.
On an individual beatmap, pp is based on the difficulty of the song and one's accuracy score on the song. One can try over and over to improve their performance, but only the best performance on each beatmap will count.
On an account, pp is based on the individual amounts of pp from each song, however, there are diminishing returns to encourage great performances on a few songs over mediocre performances across many songs. One only gets full pp from their very best performance.
To use the currently top player (as of May 23, 2016) as an example, Rafis sits at 12,204pp. Since players are ranked by pp, we know that's more than anyone else. Scrolling down in his profile and opening the "Top Ranks" section, we see that the song granting him the most performance points is Fujijo Seitokai Shikkou-bu - Best FriendS [Insane]. His 98.98% accuracy grants him 715pp. The next song, rated at the song level at 708pp, is granting his account 673pp because the second best song has a weight of 95%. As you go down through the songs, the weights continually decrease, with the total contribution after applying weights eventually summing to the overall account score of 12,204pp.
https://osu.ppy.sh/wiki/Performance_Points
Best Answer
The beatmaps that are included when you download Osu! for the first time are the following: