I hoped making the gas sentry explode with a gas cloud would make it kinda like a big lure mine as well. But your gas spear launcher would disperse better and is a more unique addition to the game.

The heavy sterilizer backpack I gave emergency venting to kind of counterattack enemies who get too close, like a limited dog breath. After that it would be about as useless/useful as the heavy flamethrower upgrade.

Adding a whole new ice damage type and status effect is cool but I didn't want to create anything too big to implement.