Friaza

When your screen starts turning red and you hear something crash, that’s the indicator that the Friaza World Boss has spawned.

Friaza starts with 0.1% power and gets progressively stronger each time someone kills him.
0.1%->1%->10%->100%

Luckily, you do not need to defeat him in order to get drops. Once he reaches 10% power, you can simply wait for Friaza to get bored and leave on his own (which he will do if there is no one left to fight around him).