Continuity mistake: When the first Spider-Man is thrown into the car and bus, he uses the street lamp that's hanging over the middle of the bus to lift the car up with his webs; however, in the previous shot, the street lamp is near the rear of the bus and isn't really close enough to be hanging over it. It completely changes position to fit the action.
Continuity mistake: From the flagpole, Spider-Man pins 2 goblin soldiers to the building and his web covers their torsos, including their shoulders and all the way up to under their chins. When it cuts to the close up, they're still stuck to the wall, but there's no web at all seen, even though we see their shoulders, necks, and chests.
Continuity mistake: When Power Man is wearing White Tiger's tiara (her Christmas gift), he has it on point-side down. White Tiger grabs it with both hands and puts it on and it's now point-side up, without her flipping it. You also see it go from a partial band tiara to a fully enclosed band tiara, like a crown.
Continuity mistake: Rhino smashes through a building, while carrying the Hulk, next to the bakery with the pink facade. In the next shot the building is fine and the bakery window is broken. Then when the Hulk smashes Rhino back through the same building, there's no damage at all and the building next to the bakery says Bank and has a green facade.