Depending upon how you look at it, this is either a very simple or a very complex card. At its simplest it can be a very straightforward card to buy and play. At its most complicated it can provide many options for card play and deck construction. I suspect though it will be simple far more often than it will be complicated.
I think the place to start looking at Band of Misfits is at the card play, which is an unusual place to start. You have the choice to play the band of misfits as any cheap card in the supply. This means that when you have two terminal actions in hand with a cheap village in the supply you can play the band of misfits as a village for the extra actions. When you have no terminal cards in your hand you can use the band of misfits as a cheap terminal in the supply, and so on. This flexibility can make deck building quite simple since you can add band of misfits to a balanced deck and it will most likely remain a balanced deck, if not better. This is only true however if there is a good selection of cheap actions cards in the kingdom: something with +coins, something with +actions, maybe something with +cards or +buy, etc. Flexibility in providing or using actions is possibly the best feature of the band of misfits.
What you gain in flexibility however you could lose in power. Being able to play a mountebank is generally better than being able to play a band of misfits as either a sea hag or navigator. Five cost cards are usually very strong and the decision to buy them ahead of a band of misfits can be simple. If there are no strong 5 cost cards in the kingdom then the band of misfits might again be simple purchase since you might otherwise have bought one of the cheaper cards instead. In the middle though there will be a small number of fiendish purchasing decisions where you are effectively weighing up a strong single card against variations from a choice of weaker cards.
The band of misfits doesn't need any specific kingdom cards to work and will behave differently in different kingdoms. The better the variety of cheap cards in the supply however the more chance the band of misfits has to provide value. You might draw a hand that could use a chancellor, or a bureaucrat, or a thief, or a shanty town, or a remodel, or a cellar, so never rule any card out even if you wouldn't purchase it for that particular deck. Even a feast could even let you gain a duchy on the last turn. Taking that concept further, the more dependent a card is upon any specific hand the more benefit you can gain from having band of misfits in your deck instead of the card itself. Specific examples might be
- cards that rely heavily on the draw such as baron or coppersmith
- cards you might only want to play early in the game such as moneylender or trader
- cards you might only want to play for late game vp such as bishop or feast
- cards you might only want to play to redress an opponent's attack such as watchtower or lookout
I will however single out a few kingdom cards. The option to play the band of misfits as a death cart will be strong, especially when you don't want to add two ruins to your deck by gaining a death cart. Throne room and procession are two cards that are heavily reliant on good draws but can provide more value than another 5 cost card if you can play band of misfits for their action in the right hand. Band of misfits will suit conspirator decks since it can either start or continue the conspirator chains, reducing the risks of bad draws, and you could well be willing to pay 5 or 6 coins for these engine components anyway.
The conspirator deck does highlight one risk though. Once a card's supply pile is empty the band of misfits cannot act as that card. This will affect key cards like conspirators but also some common utility cards such as villages, particularly in multi player games. It is also worth remembering that the band of misfits cannot act as silver. Sometimes a simple silver will be better in hand than a versatile action card, especially if you find yourself repeatedly playing your band of misfits as a low reward +action card.
If we return however to the card play we can see where the final complications come from. Band of Misfits increases the potential card plays from a hand, since you not only have to sequence your actions but now also choose what the actions are. Whilst this may perplex artificial intelligence I suspect that human intelligence will enjoy the challenge.
Edit - incorporated some valuable feedback into the article 26/11/12