Expected refers to total number of attempts a player can expect to need in order to receive at least one of each drop associated with the respective values. Nearly Guaranteed refers to the total number of attempts a player needs to obtain a 99%, 99.9%, and 99.99% probability to receive at least one of each drop associated with the respective values. For more detailed definitions and information on how these number were obtained, visit here.
This arcane was originally dropped in The Jordas Verdict. Following Update 22.14 (2018-03-01), all Trial missions were removed from the game and the arcane drops in turn were moved to the Eidolons instead.