Let’s jump to the real meat of the battle, JLA vs. Stay Puft Marshmallow Man.
In the movie, this form is rather slow. All he does is lumber down the street and climb a building. While Stay Puft appears much quicker and more agile in the game, I don’t think it’s enough that the Justice League couldn’t handle it. The airborne members might get swatted around a bit, but they don’t seem to be in over their heads here.
Like the Ghostbusters, I wouldn’t be surprised if the Justice League initially tried to simply “roast” their foe. Superman would unleash his heat vision and GL would fire a beam from his ring. Just as the proton streams didn’t really do anything, I figure the end result would be the same here.
One thing I’m having a hard time figuring out is how physical impact would affect Stay Puft. Yeah, Batman and Flash wouldn’t be able to do any significant damage, but if Superman or Wonder Woman were to punch the Marshmallow Man, would that hurt it? My first inclination would be to say no, he’s made of marshmallow; it would be like punching a pillow. On the other hand, there is still a being there to be hit and judging by the facial expressions Stay Puft makes, it is capable of feeling pain.
Another tricky thing is how the heroes actually beat Gozer. In the movie, the Ghostbusters had to cross the streams to reverse the particle flow through the gate. Now, in the game, you’re able to beat Gozer in a direct fight, but that was a form brought about through a different ritual and Egon even explicitly states that it’s a much weaker form. For the sake of simplicity, let’s just say that Stay Puft was brought about the same way he was in the movie.
As such, a direct fight wouldn’t work and they’d need to find a way to turn the inter-dimensional door the other way, just as the Ghostbusters did. Obviously, they don’t have proton packs (and no, I won’t submit to the idea that Batman had time to prepare and built some ahead of time), so another strategy would be needed.
It’s possible that enough sheer force could do it. If Superman unleashed his heat vision at full blast, and Green Lantern unleashed the full charge of his ring on the portal, the results might be the same.
If that doesn’t work, they could just call on Dr. Fate to come up with a spell to do the job. It’s a cop out, I know, but the DC Universe has no shortage of heroes, and it is something one has to take into account. If it makes you feel better, a spell like that probably would require a lot of time to prepare and execute, meaning that the 7 would still have to hold their own for some time as the mystic goes about his business. Which brings me back to my earlier question of how much they can actually hurt the thing.
In the end, the Justice League would probably win. Gozer’s no slouch, but I don’t see enough to give him a real edge in this fight. It’s still an interesting match up though. I also think that this is one circumstance where even Batman would be flummoxed. He has contingency plans for all sorts of scenarios, but I doubt “city being attacked by 100 foot marshmallow man” is one of them. That image alone makes the whole scenario worthwhile.