Where's the reason to try this build, what's the fun in it?
This build is strong enough to fight through all the current endgame situation. It is not as easy as the face puncher build or pure grenade build, it need tactics and calculations while playing. Some of you might like such play style, and some might not. BUT, if you want to fck those rocket bastards in the exactly same way they fcked with you, this is the best build for it.
What makes the playstyle of this build unique, how does it work?
The Katyusha build is by far the first build that utilize Vladof launcher, especially their underbarrels. If you check for numbers, Vladof launchers are always seems to be underpowered compare to Torgue ones. But the very key feature of Vladof in BL3 is their underbarrels, and turns out most of them are much more powerful than the main firing mod. Different from the underbarrels for pistols, rifles or snipers, most of the underbarrel for launchers actually consume regular ammo instead of use their own ammo type and have their own magazine. That is the core mechanic that makes this build work. Like Tediore build, the Katyusha build also use purple weapons instead of legendaries.
How powerful is it then?
Like I said, with maxed out gear, it fight through M3 TVHM shaft with the most disadvantage modifiers (+45% enemy HP, +40% enemy attack, no buff for the player). And with absolutely garbage roll gears, which means all weapons are not with the right part, class mod & artifact providing no relevant secendary states at all, it still defeat M2 shaft(tested in M2 TVHM shaft with a -30% elemental damage modifier, used that debuffed element intently for testing). With just one or two relevant buff from class mod & artifact, it could work in M3.
Gears and Skills
Vladof rocket launchers for damage - These are the main part of the build. You need to look for launchers by the following order: First of all, it must have the rocket salvo underbarrel. The rocket salvo underbarrel would consume 1 ammo to fire 2 rockets, each of them have closely to 3/4 of your weapon base damage. And it allows you to launcher these rockets in a full auto way, and with very fast rate of fire. That's why it is called a Katyusha build. Among all the launchers that has most base damage is the Strack, so they are prefered. You can also make this build work with Gruppa or Vred, but you should look for Strack in process of upgrading your gear. Also, you'll need to look for the largest magazine, the 18 ammo one. For other parts, just choose the one with higher damage boost. However, the x2 part should be avoided, because they decrease the damage of each rocket, and underbarrels do not get the effect of double shooting. The most favorable element would be cryo and kinetic.
Vladof rocket launchers for heal - Because rocket salvo only consume 1 ammo per shot, so you can't play the ammo trick like Scourge or Hive build. Therefor you won't use Big Boom Blast shield, and that means you'll need to heal through the mechanic of Transformer. Vladof launchers could come with an underbarell big rocket, and that rocket would heal at least half of your shield with just one shot. It performs very bad if you try to hit enemy with it, but turns out very powerful against yourself. We use that as the metod of healing. Just look for a shock elemental launcher with this Big Boy Rocket underbarrel, and the higher the base damage, the better.
A Transformer shield - As I side before, Transformer is the only viable choice of sustain, also you'll need as much ammo regen as possible for this build, and 40% bullet absorb is actually quite effective and would help a lot. So instead of just use it as a typical defense measure, it's also a key item to support your offense.
A spliting tracker grenade - Grenade hits are another important source of your ammo regen, so you want to have a grenade that could hit enemy as many times as possible. It should be at least a clusterf*ck tracker grenade. The damage output is not that important, but it better be a cryo one.
Blastmaster class mod - As long as it has redistribution on it, other skills doesn't matter, since you won't even unlock Pull the holy pin or Vampyr. For secendary status, look for +weapon damage, +heavy weapon damage, +splash damage and +magazine size. Defensive buffs are not needed compare to these damage/ammo buffs, but if you have none of these damage buffs on your class mod, something to help you live longer is also good.
Ice Breaker Deathless artifact - Cryo is the best element for this build, because this build are really not that tanky, so you'll want to freeze enemies to prevent their attack and envade, and some damage buff to kill them before they could kill you. For secendary status choice, it's essencially the same with the class mod.
With all that you are able to assamble this build.
Green tree: Get all those ammo buffs from this tree. You need both Matched set and Cloud of lead, and of course Redistribution. Something for the road is a key for this build, also Forge would make your life much easier.
Red tree: Because you could heal your shield but not your health, so go for the maxium shield possible. Experimental munitions is not a must have, so you can put it anywhere you want.
Blue tree: You'll need to max out Means of destruction, but avoid Fire in the skag den, because you don't want your healing rocket also damage you. Plus Grizzled will help you to active Something for the road more often.
Anointments could be greatly useful for this build, because you'll need to get on the Iron Bear to trigger Something for the road anyway. But with out Anoinments, this build could still work. For normal anoinments, look for 125% spalsh damage, 125% damage against unique enemy, and 30% faster action skill cool down. For terror annoinments, look for 50% cryo damage and the fire rate/damage one. Additional projectiles are not good for this build, because it only changes 2 rocket per ammo to 3 rockets per ammo, only provide x1.5 buff instead of x2.
1.Enemy rocket soldiers and other similar enemies are your primary target. Anointed enemy > vortex goon > badass goon > badass daddy goliath > badass zealot > badass tink.
2.Try to limit the number of badass tinks to only 1 near you. Their shot, along with other weaker enemy shots, are good to be absorbed by your Transformer. But their grenades are hard to envade if there are multiple of them.
3.Kill badass tink turrets, but ignore the normal ones. They can't really harm you, and will instead provide great ammo absorbtion. Also, enemy can't build badass turrets if there's already a normal one on the site.
4.Have a Vladof pistol with zip rocket underbarrel with your backup plan. It is possible you got struck into FFYL situation and your ammo is not enough to kill the nearest enemy. The zip rockets from a pistol will benefits from all your splash damage buff, and will help you out in such situation.
5.Get on iron bear if you see 2 or 3 dangerous enemies ahead of you. Move with your iron bear to find a good position to fight, and get out, obliterate them with the snow storm of your rocket salvo.
6.Avoid wide open areas, this build is not tanky enough to take damage from all directions. If you are surrounded, use iron bear to safely get out.
That's all I have to share! Hope you like this build, and get your revenge, comrades!