EDIT: Just got back into warframe after a huuuuuuge break. This stuff is outdated as of Damage 2.0. I should probably fix it some time.
Hey, thought I'd share some (hopefully) useful tips for the Tigris.
If you're willing to spend the time and effort to potato and forma it a few times, this weapon can perform well against heavy units from all factions.
EDIT: The Tigris can make very effective use of all eight mod slots, so forma's and a catalyst help immensely. To give an example, if you were to remove a single mod from any of the below mod setups, you could expect a minimum decrease in damage per second of 25%.
Furthermore, the Tigris is certainly not a well-rounded weapon. But you can cover for its deficiencies, as I'll explain later.
Firstly, these are the mod setups I use. By my calculations (which are hopefully correct), these setups give the optimum damage-per-clip against each faction's 'heavy' units whilst maintaining a four shot clip. They can all be achieved with four forma (I used - top row : 2 'y', bottom row : 2 '-').
Common - Point blank, Hell's chamber, Vicious spread, Burdened magazine (Rank 1), Ammo stock, Blaze (Put this in the bottom right slot to ensure correct elemental combinations)
Then add -
Grineer - Charged shell, Contagious spread. (Gives Corrosive (-armor) and Heat (DoT) status effects)
Corpus - Charged shell, Chilling grasp. (Gives Magnetic (-Shields) and Heat (DoT) status effects)
Infested - Incendiary coat, Cleanse infested (Gives Heat (DoT) status effect)
Infested alternative - Incendiary coat, Chilling grasp - (approximately 8% less damage, but has Blast status (cc) instead of Heat status (DoT)).
Orokin Void - Incendiary coat, Chilling grasp. (Gives Blast status (cc))
Tigris at a glance
Benefits of the Tigris
When it comes to actual usage, the main benefit of the Tigris is that it frontloads a hell-of-a-lot of damage straight up. This means that it's very good at demolishing dangerous heavy units extremely quickly - you can move in, click twice to unload all four shots in its face, and then move out. It should be dead. Always remember to aim for the head. To give you an idea of its potential, with the above Infested mod setup, it's capable of killing a level 60+ ancient with those four quick shots. I haven't had the chance to test it against anything higher.
Another thing it has going for it is status effects. If you hit with every bullet, you'll have a theoretical average of 5 - 6 procs per clip. Remember that clip empties really fast. This means, for example, that you'll pretty much always have the -armor corrosive debuff up against Grineer - possibly on your first shot, which will make your subsequent three shots do more damage.
And here's another thing - whilst there are other shotguns with high status chances, the Tigris specialises in Slash damage. Slash damage puts a DoT on the target. And you can have multiple slash damage DoT's affecting the same target at the same time. In practice, It's not uncommon to see five or more instances of the DoT ticking for damage from unloading a single clip. And whilst each individual DoT isn't that powerful, adding them all together they become pretty significant - especially if you get a Heat damage DoT proc as well(which is present in most of the above mod builds). Note that this is usually redundant because the target will probably be dead from your shots (up to a reasonable level, of course).
Finally, the Tigris is as ammo efficient as shotguns get. Narrow cone, high damage per shot.
Drawbacks of the Tigris
The Tigris' Slash damage is weaker than Puncture on Grineer and Impact on Corpus. In practice, this isn't nearly as bad as it sounds - if you use the right mods, the majority of your damage is coming from elemental damage. Plus, Slash DoT's are nice. From a purely mathematical perspective, because of the crazy elemental damage multipliers you can get on Grineer heavies and Corpus, you actually only do slightly less damage on them than you do to Infested.
The Tigris is terrible at dealing with 'normal' units. In practice, you'll be able to hit four separate targets in one clip, but that's hardly anything to sing and dance about. In fact, crying comes to mind.
The Tigris is bad at a range. It has damage fall off after a certain range, like all shotguns (although it does seem to have an extended effective range, like the Hek). Plus, even though the cone of fire is narrower than most other shotguns, you really do want to get close enough to hit all those pellets. You can't just spray your clip at a group of enemies from a range like you can with other shotguns.
Dealing with these deficiencies
To cover for its failings, secondary weapon choice is extremely important for the Tigris. Get something that you're comfortable with that can deal with standard units, and swap to the Tigris when 'heavy' units need to die. Maybe even slot that accursed Speed Holster aura into your frame (Come on, it's not that bad!).
I'm personally building an Embolist, in an attempt to stupidly cripple my effectiveness at a range as much as possible.
Well, thanks for reading. I hope that this was useful for someone.
Now, back to farming electric crawlers. :(.