Ninja Gaiden Sigma 2

This and Clearing the Path of the Master Ninja are the hardest trophies in the game. For the team missions, you will need an online co-op partner as the missions after Mentor 04 are impossible to finish with the offline A.I partner, because the A.I is terrible after this point. You can find a co-op partner in this thread.

There are 2 ways to approach these missions. One being the hard way, becoming a Ninja Gaiden veteran and killing everything yourself, learning the game inside and out. The other one being the easier way, which in my opinion, makes this trophy much easier than clearing the Master Ninja story. More precisely, there's a move in the game that makes you completely invulnerable to any kind of attacks while you are performing it called the Rachel Twirl.

Now since a trophy guide is made to teach you the easiest way to obtain the trophies, I'll be explaining the easier way. Here's a video guide for Rachel's Twirl (credit to FusionZX for the video):

I advise using the first method, the circle twirling because the other 2 methods require timing and are therefore ruined if you encounter online lag. If you have learned the Rachel Twirl, you'll be able to use it on every single MN and UN mission except for MN4; on MN4 your task will be to spam Rachel’s machine gun and move away when enemies get close to you.

All you need now is a good partner who can kill the enemies for you while you are baiting other enemies. It will also help if you are good at killing Elizabeth with Rachel's Ultimate Technique as she's tough to defeat in close combat. It's a great relief for the boss killer in UN1 if the twirling partner can defeat Elizabeth on their own.

If you are really having trouble beating UN2 normally/using the twirl, there's a glitch to get out of the hall using a combo of Momiji and spam Rachel/Scythe UT's to beat the entire mission. I advise you use this as a last resort as it is very long, boring and unnatural. Video demonstration (credit to hades68 for the video):

The combo input for Momiji to get through the wall: Double jump, run up the wall, , , hold while pointing left stick towards the wall in the corner.

For a very detailed strategy guide on all Master Ninja and Ultimate Ninja missions, check out SnapGW's Team Missions Guide.

Good luck!