A Warning message often occurred before a boss fight in the Mega Man series, starting with Mega Man X4. It generally has an alarm sounding with the word "WARNING" appearing on the screen, sometimes a voice saying the word repeatedly.
Mega Man series
Although the warning did not occur in any of the Mega Man classic games, it was included in the remake Mega Man: Powered Up, when the player was about to fight one of the bosses.
Mega Man X series
Its true debut was in Mega Man X4, where it had a periodical buzz warning as the letters spell out "Warning", the screen flashes, and then the letters disappear again. It will continue to be used in this manner up to Mega Man X6.
In Mega Man X7, the Warning is depicted as a purple border with a flashing red Warning sign in the middle, as well as the announcer announcing the word twice. It is also the only standard Mega Man X game to place the warning immediately before the battle instead of simply before the pre-battle scene, something that would be more prevalent in Mega Man Zero onwards.
In Mega Man X8, the Warning is depicted as a flash of red as well as the warning label popping up, with the announcer announcing the word twice.
In Mega Man X: Command Mission, the warning letters will fly by before forming the words as the alarm starts blaring. Because of the nature of the game being an RPG, it also takes place immediately before the battle instead of the pre-battle cutscene.
In this series, the warning segment plays before conversation with the boss battles.
Mega Man Zero series
Starting with the Mega Man Zero series, the warning will play immediately before the battle starts, instead of prior to the cutscene where the boss arrives. In each installment, the warning sign appears with the letters forming before lines appear above and below the warning sign, and then a three-boop sound effect is heard before the warning disappears.
Mega Man ZX series
Like in the Mega Man Zero series before it, the warning will play immediately before the battle starts.
In Mega Man ZX, the warning label appears, with the screen briefly flashing red in a static-like manner as a long drawn-out alarm is heard.
In Mega Man ZX Advent, the warning label appears, with the screen flashing red twice in sequence to an alarm blaring.