Some questions:
- Is it possible to make the Sackbots lethal without applying electric, flame or plasma tools to them? And not put Creatinators on them.
If you want it to be instantly lethal, you could set up a follower on poison cloud to mirror a sackbot's movements. Sackbots could also use the throwing glove and throw things like bombs or throw players into pits, but that's probably a lot more work. Also in the "a lot more work" category is driving vehicles, which sackbots could do.
- Is there possible to increase the Sackbots running speed as time increases? Like the Sackbots starts to run slow, but then they gradually gets faster and faster?
I would recommend having a "changing room" where they can enter and be replaced by a faster sackbot. If you're willing to use logic to exercise 100% control on a sackbot's movements, that would also work.
If you don't mind ganky stop and go movement and you don't have to worry about the sackbot falling (since falling could end up also being stop and go), you could put a gravity damper (leave the gravity alone but have it dampen movement) on the sackbot and have it turn on and off more frequently at the start and gradually reduce the amount of time it's on.
- How do you start a level with only one life, and when you (and all the other players) have died once, you get automatically to the score screen? (this method is often used in arcade-like levels).
You could either destroy the checkpoint/level entrance after all the players are in the level, or you could roll/drop it to where the scoreboard is.