Just tried the new hunting grounds for this week. Mission 5, part 2 was something I've never seen before and it was on the Shenzen football map. I'm guessing that it's completely new because its the first time I saw a mech so large that it could be mistaken for a kaiju. It was a bit confusing at first, but also fun.
Basically, a giant mech spawns, large enough to make the largest titan look small, and it heads in your robot's direction. It starts firing when in range. It will respawn itself to a usual PvP starting point from time to time. Not completely sure of the conditions under which the respawn happens. It looks like you'll need to do very close to a full clear of the mission if you'd like to platinum the mission, which means taking down Mr. "Kaiju" Mech and all or almost all of its hench-mechs. It did quite noticeable damage to my harpy, which has fairly light defenses. I can't say how threatening it might be to a better defended robot or to a titan.
For strategy, at first I tested things out for a couple of minutes while pouring as much damage as possible into Mr. Kaiju Mech. Then I started circling around the map to take out all the hench-mechs and eventually settled on top of the very tall and long structure on one side of the map. It's the structure with an upward arch in the middle. From there my robot and its hawkeye drone had a birdseye view of the ground below. That was a fortunate choice, in the end, making survival easier and allowing a good opportunity to pour lots of damage into Mr. Kaiju Mech.
Mr. Kaiju Mech couldn't go under the structure, and so it had to hang out nearby and hope my robot would stick its head out far enough for it to be a viable target. That allowed positioning so the hawkeye drone could keep firing and my harpy could fire when durability allowed. In the end, no titan was needed. Still, careful management of my harpy's durability was needed to avoid having it get smushed like Godzilla smushing a small freight train.
FWIW, in case it helps.