When you're guarding attacks, you also have access to G guardians, discard a heal trigger in your hand to use them. After being placed on guard circle, G guardians have a shield of 15000, but they also have a skill that if for-filled, boosts the shield to 20000 or even higher, they also count towards GB skills after used. Remember that just like any G unit, they can only be used if both vanguards are grade 3.