It is better to start with the simplest possible solution and go on with the most sophisticated solution, but for now I will just say what needs to be done:
1) We have a big monster, so we want to leave all the monsters free to run around, and to avoid getting trapped.
2) We still want to see the big monster, so we want to keep a healthy mass of people as bait.
3) We need to make sure there is at least one large monster. Maybe it's only a few. Probably it will be a couple of dozen, so we need at least two large monsters. That's all.
4) We know that there are some people that can't die here, so we need to have a lot of them, so we need to have some.
5) We have a lot of things that can't ...