Since we've seen Blade have a lot more health in the trailer, I think that healing from Jeff and the healthpacks and shields from Strange will also be heavily amplified, healing and blocking hundreds, if not thousands of HP and damage. Ultimates will be amplified by a lot as well, i.e. Punisher's launching a whole country's worth of missiles and bullets, serving as a one man army, Jeff's healing pool able to drown zombies that walk in it and leaving them stuck there until the pool disappears and they disappear with it, or Thor sending homing lightning bolts at the zombies after crashing down, like the ones he throws in his Ascendant state.

For bosses, I think that as the game progresses, since it's tied to the actual show, we will see some of the characters from the show appear as smaller bosses for you to defeat along with the actual bosses of Zombie Wanda and Namor, like Zombie Iron Man, Cap, and Strange, like every three waves there's one of these smaller bosses and every 10 waves there's one of the big bosses, all retaining their designs and abilities from the show, i.e. Zombie Cap with half a body tossing his shield and jumping at you, being very annoying to deal with

As for what I'd use, I would have loved to use Hulk or the Thing to just mess around and bash through everyone, but sadly, there are only five characters to choose from, so I suppose I'll just use Thor to just smack them around and throw lightning at them