When you beat the game once, you'll be able to access True Vault Hunter Mode. This starts the game over but retains all your levels, skills, and equipment. Areas will be scaled to your level the first time you enter them, so right from the start, you'll be fighting bullymongs in Southern Shelf probably somewhere in the range of levels 30 to 35, depending on what level you were when you beat Normal Mode.
Enemies in True Vault Hunter Mode are usually renamed and often look different than their normal counterparts, and they are always harder-a multiplier enhances both enemy health and enemy damage output, entirely new monsters will threaten you with scarier attacks than those contained in a normal playthrough, and Badass variants are more frequent, sturdier, and nastier than just your regular old Normal Mode Badass. This is not to say that those Badass guys in Normal Mode aren't still very mean; they're just not quite this mean. Still definitely Badass, though. Just not quite as Badass.
Of course, harder enemies and more Badasses to kill equals more loot, and bigger ex. gains. You'll get guns so good in TVHM and be so happy that you won't know what to do with yourself. And the outrageous power and features of high-level guns will be just in time to take on the toughest versions of Pandoran denizens.
How not to die in TVHM.
With heartier enemies inflicting heavier damage and taking much longer to kill, you may be wondering: will it be harder for me to stay alive? ("Me" in that questino meaning "you," since you are reading this aloud, right?) Yes. Yes, it will. Get caught out in the open against groups of peon enemies, or take a good clean shot from even one TVHM Badass, and you'll be testing the limits of your shield more or less immediately. Another moment in the open, and you're in Fight For Your Life. in other words, you have little margin for error. So, how to stay alive in the wilds of your second playthrough?
Shields. For starters, invest in Shield Recharge Delay and Shield Recharge Rate. If you have a shield that begins recharging at a rapid rate after just a couple seconds, then even when you get your shield busted, all you'll need to find is a few seconds' respite in cover somewhere. Get to sprinting!
Skills. Higher levels mean more skill points for good builds involving impactful gamchanging and capstone skills, the skills that fundamentally alter a character or that finish off their skill trees. At level 31, you'll have earned enough skill points to make it to cap off one tree (you'll spend most of Normal Mode without a capstone, if you even get there before the game completion; although TVHM is more difficult intrinsically, in some ways combat gets easier because capstones are so good!) At level 42, you'll have earned enough to cap off one tree and make it to the third tier gamchanging skill in another! A honed build combined with the weapons to match and a good gamplan can overcome just about anything. So while the enemies will have upgraded, so too will you.
Healing. Maya's Harmony tree has abilities that allow her to heal characters just by shooting them-it puts her Phaselock Action Skill to use as a mobile medic, reviving downed friends from afar. (In fact, having Harmony tree skilled up to the Res gamchanger might be a soft bar for admission for Sirens into high-level co-op parties.) Every character has skills that enhance their own survivability, whether throught enhancing Shield Recharge Rate and Shield Recharge Delay, expanding health and shield capacity, and reflecting damage, or even lowering the likelihood that receiving killshots will actually result in a downed state, or absorbing health from enemies somehow.
Slag. Slag, Slag, Slag. Slag, new to Borderlands 2, doubles the amount of damage the Slag victim receives from non-Slag sources. Like other elements, Slag can be applied by certain weapons, skills, and grenades. With the health multipliers enemies get in True Vault Hunter Mode, especially the multiplier gained be TVHM Badasses in four player co-op (x8!), Slag is absolutely essential to True Vaul Hunter Mode. If you're playing solo, then have a Slag solution - use Slag grenades on groups, or always have a reliable Slag weapon in one of your equipment slots, or inflict Slag with capped-off Action Skills like Maya's Scorn melee or Ruin Phaselock and Axton's Double Up Sabre Turret. It's easy to tell a Slagged foe - a purple sheen covers them. Focus your efforts on Slagged enemies, especially Badasses, and remeber that Critical Hits still count and stack with the Slag double damage bonus!
Teamwork doesn't just mean defense and triage. Having one teammate focused on applying Slag to everthing with a pulse is a big weight off the mind of others in the group; having someone ready with an Electric grenade or firearm for the shielded enemies will be, too. In areas with rakks, Sky Hunters, Repair Drones, and Surveyors, one friend might hang behind the rest and focus on keeping theskies clear and sniping from afar.
Crowd control is even more valuable. Action Skills do most of the work; Axton's Sabre Turret harasses and distracts enemies every time he deploys it. If Salvador builds up the Brawn tree, the Come At Me Bro capstone allows him to become a tank for the entire party at will, the belle of the ball and the center of the collective attention of the assembled enemy with the beckoning of both his middle fingers. Maya's Phaselock always takes at least one enemy out of commission by definition, and it can be made to distract much more than that - Converge pulls many targets into the main Phaselock victim, and Thoughtlock causes the assembled foes to fight amongst themselves. (Any character can create a Converge effect by using Singularity grenades, too!) And Zero's Deception decoy attaracts the attention of many, as Zero himself zips around the battlefield cloaked and unseen. Any enemy who is distracted, stunned, locked up, tied down, or otherwise incapacitated is an enemy who is not shooting at you or your co-op partners, so managing the enemy's attention is key to staying alive, and it is one of the beautiful ways the different classes fit together.
Conflating advantages. A target afflicted with Slag takes double damage, and Critical Hits from the right weapons, like a sniper rifle, can score four times normal damage or more. Using the right element for the job stacks right on top of those, too - Fire on flesh, Corrosive on armor, Electricity on shields, Explosive on crystals and Nomads with old-fashioned shields - and that's before counting the bonuses to any or all of the aboue you'll receive from skills, class mods, Relics, and bonuses from the class mods and Relics of teammates in co-op games.