This is in the new update, You only get access to the map at grand master with your level 200. The new max level is 210 so that's why they added this map for 200s. You only get xp at 200 in this map. You can't play it in single player, and it's not in the default maps, it's on special. The bosses are very strong.
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Also thank you for those who helped with the boss.