I can summarise the benefit of including Blackjack in your deck in one word: consistency. I'd argue that it is the single most consistent weapon in the entire game, as is espouses multiple facets of that virtue:
- It's cheap, meaning that you'll be hard pressed to not be able to play it from the moment it enters your hand.
- It's has unlimited usage: no "uses: X", exhaust, or discard conditions.
- It eliminates the difference between an attack on an enemy in some else's threat area and an attack on an enemy anywhere else.
Arkham Horror has a wonderful unpredictability to it, that often means your best laid plans when crafting the ultimate deck will not survive first contact with the mythos. Everything from the catch-22 of not being able to play a weapon without incurring an attack of opportunity from an engaged enemy, to the unpredictableness of where any enemy will show up, who it engages, and what dastardly text will be written on it to counter certain investigator staples. To those that have been burned too many times by this damnable chaos, Blackjack will offer some reprieve.
Is it a good weapon? Hell no; it's a one cost asset after all. With no zero cost weapons in existence yet, Blackjack represents the bargain barrel deal of armaments. But it's cheapness is a strength in it's own:
- Discarding assets is a worryingly common punishment that the mythos will mete out; the best counter to this is to offer a cheap tribute that will keep you far more valuable allies and weapons around, like Blackjack.
- You may want a few extra weapons in you deck to increase the likelihood of drawing one at the start, but if you're already strapped for cash, a cheap card like Blackjack may be able to buy you time until your better weapons show up, and until you acquire the resources to play them.
In the end, this card isn't going to be a part of any fancy combo, nor the centrepiece to any deck, nor the subject of a memorable moment in your Arkham Horror career, but this does not make it a bad card, just a boringly average one.