World bosses are server events, not private quests. The published rule is a 20 percent chance every 3 hours across all servers. Server hopping does not roll the timer again. Each boss has a map-wide warning before the fight.
The boss index said Earth was the only location and listed five bosses. That sentence may predate later content. Namek is the current official expansion, and the Halloween event also added raids. Use the five writeups below for the fights that have public mechanics, and treat anything else as unnamed until you see it.
Lord Slug
Snow across Earth means Slug is next. His minions fly in from around the map and gather. Fight that group to make him spawn. You have 15 minutes before his enrage freezes the planet and kills the server.
Phase 1 goes down to beams. At zero he fully heals, grows, and enlarges every hitbox. Stay on projectiles in phase 2. Melee in an uncoordinated crowd is how players hit each other. When phase 2 ends he retreats and the snow stops.
Drops include Super Explosive Wave, Eye Beam, the melee move Disrespect, False Super Saiyan, the Namekian giant form (also called Great Namekian on the drop line), Eternal Youth, Gum Gum Rocket, the Slug Soldier Z-Assist, the titles Slug Demon Clan and Subjugator of Stars, and the Slug Demon Helm.
Turles
The Tree of Might appears near West City and its roots cross Earth. Defeat the Crusher Corps before Turles himself can be fought. Phase 1 ends when he eats a fruit and starts Force Explosions, Sudden Storm, and Finger Blast. There is no published time limit. He despawns the tree after the second health bar. Drops are Calamity Blaster and a Tree of Might fruit that buffs stats by 50. The page does not say whether 50 means flat points or a percent.
Friaza
A red screen and a crash sound mark the spawn. He starts at 0.1 percent power and steps through 0.1, 1, 10, and 100 percent each time someone kills him. You do not have to kill him for loot. At 10 percent he can get bored and leave if nobody is still fighting. The Saiyan drop is Legendary Super Saiyan. The title is Universal God.
Banaras and Super Buu
Banaras has no published spawn rate or moveset. His drops are Gigantify for Yardrat forms, Max Power for Human and Alien forms, and the Power Bomb capsule. Human Max Power is the same reward the form lists point at this boss for.
Super Buu is on the boss index and was named in the Halloween event as a world boss. A public moveset page was not available. Babidi's Ship Dungeon, the Buu Awakens raid, and the Gotenks raid were announced in that same event without fight steps.
How to show up ready
Bring a projectile you can fire while other players take the center. Do not open a long transformation on the adds if you need the form for the real health bar, and remember transformed damage reduces NPC payouts on ordinary quest mobs. Boss drops are forms and capsules, so the payout rules for random enemies are a separate question. If the warning is snow, a tree, or a red sky, go to the gather point immediately. Slug's 15-minute enrage is a server wipe, not a personal fail.