Having a way to ramp mana for white decks is a true game-changer, so long as this card stays on the board
For example, if it blocks a 12/12 creature with trample, that creature's controller must assign at least 8 of that creature's combat damage to Diamond Weapon, and the remainder can be assigned to the defending player, planeswalker, or battle
The card gets even better with its second ability, letting you pay three mana and tap it to draw two cards
Alternatively, use a service like MTG Print to print your proxy cards on your home printer
A free edict, essentially, that you pay for like a lot of other edicts, by sacrificing your own thing
You get to deal X damage to any target and then score a chocobo that grows with your land drops