For competitive, the most useful cards are probably Leaf and Mew Ex, maybe Serperior and Celebi Ex if they ever become meta again, but not much else
Regardless of what cards were added in the flex slots, the deck won by playing out a massive number of creatures, attacking with them, and then sacrificing them to drain out their opponents with [card]Blood Artist[/card] triggers, amass an army of flying demons courtesy of [card]Skirsdag High Priest[/card], or just create a giant [card]Voice of Resurgence[/card] token to bash their opponent to death with
Swan Song hits most combo pieces and value engines while it only gives away a harmless 2/2 bird token
Jaheira, Friend of the ForestJaheira, Friend of the Forest: Since this deck is playing Craterhoof BehemothCraterhoof Behemoth, Decimator of the ProvincesDecimator of the Provinces, and End-Raze ForerunnersEnd-Raze Forerunners (Not to mention Kamahl, Heart of KrosaKamahl, Heart of Krosa and Living HiveLiving Hive), we need a lot of mana
When you bear the sizeable price-tag hovering over the card in mind, this probably isn't surprising
So the more creatures you have the bigger they get