I can confirm Shiver + Blitz destroy fiends. They can't aim at you if they are frozen.

Apart from that, I can't see any real other combo.

Shiver does shut down Fiends of all stripes (stopping Trojans from turning, Devilites from dodging, Greavers from chasing, and Silkwings from moving toward damaged enemies), except for those nasty Freeze-themed Fiends. As these infest Heart of Ice like a plague and also are present in The Gauntlet, it's almost necessary to find something else.

DBB works well on its own; stay at a distance where you can hit them with the edge of the blast, then drop it after the Fiends' throw. The blast will interrupt Devilites. Alternatively, you can kite the Fiends into a Sun Shards blast, then mow them down with relative ease. Stagger Storm might also cut it, but watch out; it has a very low Stun time. Greavers are a bomber's nightmare, since they attack quick and can only be interrupted by being hit; however, shielding in your own blast radius can hold off their damage while you then prepare another bomb. Just watch the mist clouds they generate, especially Shock and Freeze.

As far as guns go, the Blitz is tough to use; don't underestimate the normal attack against fragile little rabbits like Devilites, though. If you have someone shield-screening you, Shivering, or otherwise being a most excellent distraction, a well-placed charge can decimate Devilites. Alchemers also might be useful; despite their non-Piercing damage, they can hit a Greaver closing in on you and then ricochet off that Greaver to hit another Greaver. They also are good for killing Undead, which tend to come along with Fiends. Alternatively, the Argent Peacemaker is mobile and easy to use in a pinch, though it doesn't have the Alchemer line's potential.

Aside from that, people like the Barbarous Thorn Blade and Final Flourish, and I can see why; it's fast and it does great damage on Devilites. For Greavers, I always liked Heavy Swords like the Divine Avenger and Sudaruska; the wide arc of each swing can hit many of them at once, and the raw damage will put a massive dent in their HP total, and if you're sure you won't be hit, the second swing will hurt them even more (or you can turn around and hit that annoying flappy little upstart that came from behind you).

Vortex has the same charge time as nitro. It only feels longer because of the slower movement. It's the same effect as with Irontech.

I just tested it, and I appear to be wrong. They charge at haze bomb speed.

3* vortexes charge at blast bomb speed, though.

A few things I don't agree with :
"I think shivermist is a good bomb, but IMO some people rely to heavily on it. Maybe it's just because I'd rather kill enemies than trap them."
I generally agree with that, but not for devilites. It way quicker to kill them if you know they can't fight back : you don't have to shield and can actually do full combo / blitz charges. And not having to shield all the time when moving is a big plus too.

About Blitz : it's great on large groups too. You have to remember it outrange devilites by 1/2 blocks. When you know that sweet-spot, it destroys any pack of devilites safely. It may not one shot them, since only 2/3 bullets will hit each devilite, but on the other hand you have a very large width, and it's really safe : either devilites attack straight and miss, or take time to move and they will be interrupted before finishing their attack. Don't forget about coordination with a shielder too. I do use both those techniques in Heart of Ice.

Even though it's narrow, you can even shoot without aiming exactly at their position. They sometimes do many sideways dodge (bullets) that they got themselves into those narrow cones even your aim was off. Offscreen hits are most likely from below (which you can prevent by keeping most groups of monsters above), since you cannot see well below part of your knight.

Devilites -> Magma/Hail/Storm Driver or stun/piercing shards

Trojan/Griever-> Blitz/Plague/Pepperbox/Callahan or Dark Briar Barrage/Nitronome

Blitz's wide charge attack angle, long range, and massive damage makes pretty easy work of devilites. When attacking with a blitz a maximum range, it's quite likely that they will in fact dodge into your bullets and also deal enough damage to interrupt their attacks.

It's also helpful to have to have a member shielding you or hug against an obstacle to prevent yourself from taking damage. And nevertheless you can just simply trollaris them.

As for bombs, the popular combinations I see often seem to be shiver + blitz or vortex + blitz. EV and blitz works simply beautifully on FSC. As for devilites, its also mostly shiver and sometimes haze/tempest in place of shiver especially on HoI

VT and AoA
Pepperbox/Blitz, Alchemer/Polaris/AP/Sentenza.

The two DoT bombs for, well, DoT
Blitz/Pepper for massive charge damage,
Alchemers for versitility, Polaris for CC/Knockback, AP/Sentenza for the sake of mobility.

Pros: HELLA damage. The statusing bombs might not make targets easier to hit (much), but if you spam these bombs and dodge randomly, just cross your fingers and count to 20 and POOF everything is dead (note: results may vary from user to user. Use at your own risk)

Blitz line is devastating, and can quickly clear a room, but is dangerous since of locked-in-place-while-shooting.

Alchemers provide great charge damage and are reliable in a pinch.

Polaris is for playing it safe, and for knocking back foe into the status bombs' areas of effect.

AP/Sentenza is the opposite of Blitz, and offers mobility while shooting. Lacklustered damage and no knockback make them tricky to use.

Good luck?