In the next update, you'll always get the panties of the ice raid boss first, then the memory orb. Afterwards you get the "normal" legendaries, as you can obtain from the orange chests.
The chance for each boss is the same, and is decided when you enter the dungeon. There is no "pattern" to get a specific boss, but you might be able to tell what boss will come by what things you encounter in the dungeon, since the same value affects things in the rest of the dungeon as well.
I added more drops for the green seed.
The bug for getting multiple legendaries should be fixed now.
The walktrhough was right, the order in the game was wrong. It's fixed now.