AI0: 0 (Zero difficulty, just zero difficulty...)
AI1: 1 (My grandma beats it!)
AI2: 2 (Noob's common enemy.)
AI3: 3 (Average level of an unupped deck, but why they're called 'Elders'? The AI plays more like a 'child' than an 'elder' here.)
PvP1: 4 (Usually noobs roam there, but an experienced opponent will appear once in a while for a challenging match.)
AI4: 5 (Half-bloods, half-upped, half-unupped, one-and-a-half health, Element's overall average difficulty.)
AI5: 6 (Powerful, but if you know your enemy you can beat him/her. They're 'Gods', but they're 'False' too.)
Bronze: 7 (I put it here because a lot of people keep losing on purpose versus AI1 in order to build Bronze/Silver decks instead of Golden/Platinum ones and their decks are full of shards and upped cards. Nowdays, I can't hold my rage when I encounter a Bronze deck which uses SoF or SoSac.)
Silver: 8 (People behave here with the same way they behave at Bronze, but the overall level is much greater)
PvP2: 8 (Manytimes noobs with fully unupped decks appear, however the true PvP duel is trully challenging with fully-upped-and-full-of-shards decks used by worthy opponents.)
Gold: 9 (Powerful decks made by experienced players who exploit everything to annoy you to death, that's what Gold League is all about. Oh look, another Ghostmare!)
PvP Events: 9 (You may use mostly unupped decks, but your opponents will likely be veterans of the game. Because of that, PvP events always push you up to your limits.)
Platinum: 10 (All hell has broken loose! Platinum decks become more and more powerful day by day. They always were impossible, but now they are... -_- )
