2.1.1 Season 1 Legendary Gem Leveling Guide

    Speed Leveling Legendary Gems

    Gem Upgrade Chance / Greater Rift Level Compared to Gem
    ----------------------------------------------------------

        0% / -7
        1% / -6
        2% / -5
        4% / -4
        8% / -3
        15% / -2
        30% / -1
        60% / +0
        60% / +1
        60% / +2
        60% / +3
        60% / +4
        60% / +5
        60% / +6
        70% / +7
        80% / +8
        90% / +9
        100% / +10

The most efficient way to get a level 25 Legendary Gem would be farming "9" Greater Rift Trial Keys, which drop off normal rift guardians/bosses. Than proceeded to complete Greater Rifts Level: 12, 15, 18, 21, 24, 27, 30, 33, 36; Which allows a 100% chance to upgrade your gem to tier 25 | PS. don't forget to hit upgrade gem every time you complete a greater rift

Trial Wave in relation to Greater Rift Keystone awarded
----------------------------------------------------------

Solo: Trial Wave - 3 = Greater Rift Keystone awarded
Ex. If you completed wave 20, you will receive a level 17 keystone

2 Players: Trial Wave - 4 = Greater Rift Keystone awarded
Ex. If you completed wave 20, your group will receive a level 16 keystone

3 Players: Trial Wave - 5 = Greater Rift Keystone awarded
Ex. If you completed wave 20, your group will receive a level 15 keystone

4 Players: Trial Wave - 6 = Greater Rift Keystone awarded
Ex. If you completed wave 20, your group will receive a level 14 keystone