Introduction - Welcome to Hell!
Okay, this actually WON'T be a comprehensive guide, 'cause I feel Acolyte through Mentor should be easy enough for ANYONE to handle, provided they give any "tough" missions a couple of tries. However, the Master Ninja (MN) and Ultimate Ninja (UN) missions are almost universally finished last, and only after dozens and dozens of attempts, each. Some in the hundreds. I've played the missions enough, that I've learned a few key tricks that I wish to pass on, so the rest of you will have it a bit easier!
Gross Generalizations
Team Missions LAG! Depending on the day and time, what you have on in the background, and how active Murphy is, your overall lag will vary. Sometimes short lag bursts will interrupt a combo, or the overall pace of a mission, resulting in a freak loss. These are usually unavoidable, but for the most part, timing your commands and compensating for the delay will solve any issues. In some rare instances, lag may be HELPFUL, when it makes certain enemies appear to be moving in "slow mo", allowing you to dodge more easily! Sigma 2's lag MIGHT leave you feeling hopeless, but it IS something you'll get used to, trust me.
Kills with Ninpo almost ALWAYS leave behind Blue Essence! Take advantage of this. When you're surrounded by obscenely large numbers, and your health is low, an Ultimate Ninpo could possibly refill your health bar, provided you and your partner divvy up the essence, accordingly. Depending on the enemy killed, you might even get a Red Essence orb to replace the Ki you just spent! Plan your ninpo usage, accordingly, and reserve it for the times you NEED it!
On-landing Revive = QUICK REVIVE! This trick is invaluable. As you'll play through these missions, you'll run into MANY instances where you go to revive your downed partner, only to instead start tossing projectiles and leaving yourself open. Quick Revive almost always works without bugging into the wrong command. Execute it the same way as an On-landing Ultimate; jump and tap the button as soon as you touch the ground.
The host has the enemy's attention, at the mission's start. While not always true, often times the host will be the default target at the start of the mission. This means the invitee can usually "sneak up" behind certain opponents and get easy hits/kills without need of timing a counterattack. In instances this rule doesn't apply (like UN1 or UN5) there's still a similar situation, in which certain enemies ALWAYS target one player, and certain enemies ALWAYS target the other. Providing your connection allows, you can use this to your advantage and plan who hosts and who joins, matching each "position" with the character each player uses, per mission.
Don't forget about your projectiles! There are 5 unique ranged attacks to choose from, 2 of which Ryu can use simultaneously. The bow is a versatile weapon that strings seamlessly into combos, and takes down dangerous ranged opponents quickly. Rachel's gun can make short work of many waves of enemies, provided your partner distracts them for you. The Howling Cannon can hurt certain bosses, making it an effective means to safely deal damage in otherwise tricky battles. Shuriken can even cancel out certain attack animations, making a dodge or follow-up combo a few frames quicker!
Auto-camera is NOT your friend! Sigma 2 VASTLY improved on the 360 version's camera problems, but ultimately, its automated boss camera still suffers from serious deficiencies. Because of this, AND the fact that you CAN'T use the Auto-cam in Ultimate Ninja missions, it's strongly suggested you TURN OFF Auto-cam in every mission you have the opportunity (press R3 to toggle). With enough knowledge of boss attack patterns, practice with the manual camera settings, as well as adjusting your camera speed, you'll find yourself better off without the auto-cam!
PRACTICE! Like it or not, you'll be replaying certain missions, repeatedly. You'll end up playing the same bosses, over and over again, to the point of memorizing their attack patterns, and tells. Elizebet and Alexei, in particular, you'll learn have the habit of changing targets, making it difficult to isolate bosses, with them around. Of course you want to complete a mission, but don't forget that every failure is just another opportunity to learn something new, or somewhere to improve. KEEP AT IT!!!
Forthcoming Terminology
Since it's easier (and saves space) to use the NAME of an enemy, rather than describe them all, it might help if you KNOW what each enemy's name IS! So, whether you use this as a "key" for the following walkthrough sections, or just fun facts that you didn't already realize about the game, here they are.
Shadow Fiend Your generic Fiend enemy from NGS, which returns in NGS2. Weak but agile, they travel in groups, fire energy projectiles from their hollow torsos, burrow underground, and surface to make devastating grabs. They appear either purple, black, yellow, or red, from weakest to toughest.
Van Gelf Large and lanky demons that pounce on you to grab you, or shoot fire at you from a distance. They also breathe deadly streams of fire when wounded. Van Gelfs come in 2 forms, flying and grounded. The gold and black variety of each, respectively, are the more deadly of the two.
Gaja Tall, serpentine, skeletal creatures. They wield dual katars with deadly efficiency, and use their long tail to grab. They can be Izuna Dropped with ease, as long as you can single them out.
Spriggan The purple, cycloptic, chainsaw and bazooka armed Ghul. Left to their own devices in the background of large battles, they can surprise you with cannon fire. Prioritize them like most "ranged attackers".
Executor The formerly human cyborgs first encountered aboard the Daedelus. Grounded or flying, they fire miniguns or rockets. Prioritize them above ANYTHING else.
Marionette Demon. Three-legged, two-headed, PINK... thing. Rarely encountered, but dangerous when they appear. Usually easily left for last in large fights.
And then there's the strategies and techniques.
BOTA Blade of the Archfiend, or Dual Katanas
I.Frame / IF "Invulnerability Frame", a state that affects the play during certain attacks in which they CANNOT be harmed. Grabs, Drops, UTs, and some attacks are IF'ed. These make for quick counterattacks, when a simple Reverse Wind wouldn't last long enough to counter some attacks.
360
A move most weapons have, which the BOTA posses an I.Framed version of. It's deadly, and protects Ryu almost completely during its animation. Simply move your L3 stick in a circular motion, clockwise OR counterclockwise (and not even a full revolution) and press
360UT A variation of UT that some weapons possess. It's charged just like a regular UT, with the exception that you spin the L3 BEFORE holding

(not during or after), and let's loose a DIFFERENT attack than the standard UT.
Looping is the process of catching a boss in a stunned "hit" animation with the same attack, thus preventing them from EVER fighting back. Genshin (human ONLY) can be Looped into an indefinite Izuna Drop with either the Enma's Fang (->




when he lands) or the Lunar Staff (





when he lands). Ryu clones can be Looped with Izuna Drops like Genshin, with the exception that you need to delay the following drop until AFTER the clones get back up, otherwise it will miss.