After they turn blue
Megaten Gold may grind your GB easily in Megaten, while in fact, grinding your GB to 5-12 is not an easy thing, you can grind vanguards and devas till they turn dark blue .This is not a bad idea. Because they drop Mansion passes, plates for mansion pass collection and even new type clothes. You can move to Beast Clan at tiger riders and next to wolves after they turn blue.