I somehow got a level 4 mortar and I can't find a setup that makes it better than any other of my existing builds. I found a small niche for it to fight melee without boosts or grapple, but otherwise there are far better options. Currently I run a Corsair with a Repulse and Cutter Rocket for my main. Unlike what the OP recommends though, I have a Bigfoot and Double Roller on it for wheels. Gives it enough health that it can straight up tank almost everything. I back it up with a Dozer with a Double Blade and a grapple to handle bots with forklifts. Despite still not having a sleigh or a freeze box, they are still enough for me to place in the top 15 of the top league.