The main idea is to keep Shelldon alive for the most time possible (20sec max duration), this way you will have to survive without him for just 10sec.

Building medball tanky makes you able to properly heal against bosses and stay on the frontline without worrying too much, you can solo tank a lot of things with that build because of the high HP and self heal together with two healing gadgets.

The build of course lacks damage, which almost don't exist there, but in trade for losing damage, you can do both tank and healer roles at same time with that amount of HP and sustain, you also can easily keep your alives alive with your weapon combo and gadgets. Shelldon is a key part of the build there too, because while he is alive he always taunt all the enemies on screen, making him be a "your team does not get targeted by anything for 20sec" and together with medball Shelldon never die.

Note: the main reason we are running Shelldon there is because we don't have a third healing gadget, so instead we use something that can protect everyone from damage.

Obs: you can also use that on maps for farming, Shelldon is still useful there.