A while ago a reader mentioned that he used Forge to playtest new decks. I thought it was an interesting comment because I never considered that idea. Forge has around 75% of all of the cards in standard (75% is just a guess) but I see how it could be a good playtesting tool. Any cards that Forge did not have, you use the developer menu and change mana and life points as needed.
Forge is a good playtesting tool because you can see a variety of game situations. It is hard to look at a card at face value and say, “This card is good” or “This card is bad”. Your experience with other similar cards may make you think that a card is good or bad but without using that specific card in a game, you cannot be sure. I have built decks around cards that I thought were great but the playtesting showed me the truth.
Forge lets you test and build decks very quickly which helps you playtest many different decks. Since the AI is very basic, you can play whole games in 5 or 10 minutes. A real life 1-on-1 game would usually take 30 minutes or longer.
On a side note, Magic has a very influential pro-tour and there could be a market for a program that lets players playtest decks. The application could be stupid and only a “virtual tabletop” that did not understand the rules. The application would allow users to make decisions for both players and at the most basic level the application would not need any AI. A simple AI like Forge would not be too difficult to code but it would need to be able to use all of the cards in standard.
Just a humble guy,