You can take out any problem card stopping you going off, winning or just living regardless of its size or card type and you can do so for relatively little mana compared to the appropriate hard removal spell for that thing
Saying a card is lightly played or having it looked at by a local gaming store and having them say it is a certain condition does guarantee that it will be seen as that condition by everyone
The cards will be there next month and the month after
Standard has many lands that provide both black and colorless mana, such as Llanowar Wastes, Caves of Koilos, and Corrupted Crossroads
No, you can't cast one of them twice - the card doesn't say you can
The early leader is the Mega Darkrai ex Mega Hyper Rare, #120, with Japanese copies trading around $600 before the English launch, followed by the Mega Darkrai ex Special Illustration Rare #116 at around $400