Greavers are easily shredded with a DVS/Striker series weapon, and they're always eager to get in your face, so lure them out when possible to cut them apart. When that's not the case, you just have to spam attack and dodge Devilite/Howl projectiles at a time.

If you're soloing, you'll want speed, as Fiends are flimsy enough as is. Damage will be redundant, but a sufficiently fast toothpick will be able to hit Devilites before they fire off an attack. I use Ultra, and that gives me a split second before they hit me.

Callahan's decent for picking off Devilites, but it doesn't have much other use. Sure, you can flinch and stagger everything in there, but only one/two at a time.

Valiance isn't terribly useful, it does have merit at taking down Howl heads, but that's as far as the real utility goes.

Pulsars are great for breathing room, but they distance Devilites, which is bad, and can only hold off so many Greavers.

DBB's only really good in a party, Greavers will hit too fast before you can get a detonation off.

As for your dilemma, try to lure the Greavers into an area safe from Devilite projectile fire, shred them, then prioritize the Devilites. Everything else should then be fair game. In addition, Freezing Souls appear in only a handful of areas, but treat them as you would Greavers. After that, murder Howls and then whatever's still walking around.

With a Flourish line sword you mostly want to stick with single swings and cancelling when Devilites are around. Sometimes you can get away with two swings before cancelling but the third will leave you too open to attack unless the only remaining foes are the target of your attacks.

The best way to handle Greavers in a messy area in general is to kite them back and swing one + shield cancel whenever they lunge at you, while continually moving backwards. If there's an area you can use to block line of sight from ranged (Howlitzers and Devilites) then hang out there while you deal with Greavers for as long as you can. Kite kite kite.

For Devilites and Silkwings you can just run in large circles around them, close in when it's safe to for a quick swing + cancel and then continue running in a circle for another loop. Devilites throw are easily flinched and their melee takes a while so this is fairly safe if done properly. You can use the same approach for Howlitzers too though you have to be more careful about when they'll shoot. Since they're stationary and you don't need to worry about them dodging into the path of your circle it's better to just shoot them if you have a gun.

As a general rule you want to avoid staying shielded for too long a period. Moving slowly for too long will leave you vulnerable to being easily surrounded and it's pretty critical that your shield isn't broken if you're ever frozen.

Frozen Souls. I hate them. So very much. As far as I can tell, you want to run away from them as much as possible. They take a while to explode once they're near you (shake for a couple of seconds) but from what I've noticed, despite what it says on the wiki, once they start shaking they explode when hit and that explosion can hurt you. While you can hit them with a sword and be outside the explosion range, sometimes they spawn on you and start shaking immediately. If you don't hit them they won't explode immediately (they'll shake a bit first) so just run though them (if needed) and away from them. Shielding and crawling away from them seems sub-optimal, per the previous paragraph.

In general my priority goes something like this: run around a while if my shield is at all damage, kite and kill Greavers, then kill Silkwings, Howlitzers (if Silkwings are far enough from a Howlitzer I'll sometimes opt to kill these first), Devilites, Wolvers, everything else. If opportunity presents itself to easily kill something in that list (like Wolvers since they can teleport to you while everything else is far away) I take advantage of that. Wolvers are sometimes annoying in large amounts since they can teleport directly in the way of where you were running but otherwise aren't much a threat.

Think that's pretty much it. The boss is easily enough to not have to spoil, and more fun seeing for yourself.

In order to succeed in Heart of Ice...

1. Fill out the Job Application
2. Take a survey with an IT Guy (perhaps even Tohru)
3. Equip the Vitasuit and Fractured Masks of Seerus.
4. Head over to Amu- Sol.
5. Accept the vendor's requests as he throws furniture at you.
6. Get through the security measures.
7. Head to the coliseum, where a welcome committee and special training will assist you.
8. Take your application through Maulos's supervision.
9. ???
10. Profit.

Try dodging a few flying weapons and you'll be fine. Now, back to reading yet another book...