"When da 'umies come. In their shinin' canz. Who yah gonna call? TANKBUSTA!" - Warboss Reff-Ranz describing the Tankbusta crew.
Many Orks enjoy the odd explosion. These guys like that so much that they decided to get into a nice squad of 5-15 boys who have the same opinion on the best thing to do in a WAAAGH and try blowing tanks sky high with their rokkits. They also train Squigs to run into tanks while strapped to the hilt with explosives.
(Like the entirety of the Imperial Guard, this idea was stolen from WW2 Russia). *BLAM* HERESY! THE IMPERIUM WOULD NEVER STEAL TACTICS! *KRUMP* DEM 'UMIES KEEP GETTIN IN 'ERE BOSS!
And if neither of that works, run into close-combat and strike the tank with a rokkit attached to a metal stick. They get so high off this that they will enter the broken vehicle, eat any survivors, and drink the motor oil in a ritual act known as "GETTIN' TANKED!" And thus the Tankbustas came to be.
Just as primitive hunters might claim a gruesome trophy from a fallen beast to better brag of its demise, so will Tankbustaz strip the choicest loot from the wreckage of a ruined tank, as any Ork finds something glorious in being able to boast about killing something twenty times his size. Colourful hull plates are hammered into crude armour, internal gubbins worn proudly as warrior jewellery, and the flayed skins of crewmen are draped round the Tankbustaz' shoulders like pelts. Within a Tankbusta mob, competition is fierce to be the first to get a kill, or to get the most impressive explosion.
As of 8th edition Tankbustas are one of the Orks' best sources of reliable anti-tank firepower, and are generally a good elites slot in any ork army. Tankbustas have the Tank Hunters rule, allowing re-rolls of all hit rolls (melee and shooting) that target Vehicle units. As such, they do a frighteningly good job of blowing up vehicles that are within range of their Rokkit Launchas. Throw em in a transport such as a Trukk or an open-topped Battlewagon and just have them drive around while firing rokkits at everything. Although the AP -2 of the Rokkit Launcha isn't amazing, this is largely mitigated by the reliable damage output of 3 wounds per hit. In short, you only need 4 solid, unsaved Rokkit hits to kill a Leman Russ Battle Tank, and that is something that a full-strength Tankbusta mob is very capable of delivering. Don't be afraid of the Bomb Squigs either, they got better AND got a price cut. Furthermore, despite the name, Tankbustas are also devastating against most Monstrous Creatures (who tend to be T5-6 with 3+ saves) as well as any expensive MEQ or worse armored models (like crisis suits, tyranid warriors, and wraithguards) and can blow up MEQs in a pinch if there's nothing else to shoot. Even against Daemons and Tyranids where you'd think they'd have nothing to shoot at, those monstrous creatures are all pretty vulnerable to S8 shots flying into their faces. And with all the rokkit shots you even have a good chance at hitting fliers too.
If Tankbustas have a weakness, it's the fact that like most Orks they are wearing a T-shirt for armor and also that any opponent with a brain will do everything he can to eliminate them.
Bomb-Squigs - The Bomb Squig counts as a member of the mob, although there is no Morale impact if one dies. The Bomb Squig carries, wait for it, a Squig Bomb. The Squig Bomb hits on a WS and BS of 2+ and the Squig is expended when "fired" (nothing happens if you roll a 1 to hit). And by expended, we mean the Squig literally blows up right after experiencing a brief moment of disappointment at not finding a tasty snack under that tank/Space Marine's boot. This attack is resolved at S8 Ap -2 D6 wounds. It is therefore possible to have a max size mob of 15 Tankbustas supplemented by 3 Bomb Squigs.
Tankhammers - The Tankhammer serves as a melee weapon that replaces a model's rokkit launcher. If the Tankhammer hits, the target suffers D3 mortal wounds; the downside is that the model bearing the weapon is killed. This probably has something to do with the unhealthy fact that the "hammer" portion of the weapon consists of about 50 pounds of high-explosive ordnance that has been duct-taped together. While a tankhammer could potentially be useful for finishing off a high-value target, in all honesty it's not a great choice. This is because it reduces the mob's greatest strength, which is shooting, while also encouraging the action that it is least effective at, which is melee. Therefore you're probably better off just using Bomb Squigs to achieve a similar effect.
Rokkit Pistols - One in every five Tankbustas may replace his Rokkit Launcha with a pair of Rokkit Pistols. These count as a single weapon that have a profile of 12" Range, Pistol 2, S7, AP -2, and D3 wounds. Whether or not you think these are superior to a rokkit launcha is probably entirely situational.
Dedicated Transport - In 8th edition it is now a very simple matter to have Trukk-mounted Tankbustas. 12 rerollable rokkits a turn out of a Trukk is dangerous- yeah, that's an understatement. And guess what, any Bomb Squigs you take can still fling themselves out of the vehicle at the enemy because they count as a ranged attack.