Squighog Boy
These boyz are a revamp of the old concept of Boarboyz as orkish cavalry. The big difference is that these Beast Snaggas ride on a vaguely boar-shaped squig simply called the Squig-Hog, instead of riding on warboars. These giant porcine beasties rampage around squealing at and biting their enemies with enormous jaws, while the Ork and Grot on back hang on tight and take swings at any enemies in range. Some Squig-Hogs may get "upgraded" by the local Painboss to include Cybork bits, ranging from everything from a bolted-on metal jaw to THE ENTIRE BACK HALF REPLACED WITH MOTORCYCLE PARTS for maximum speed and killiness.
Precisely why they were invented in the meta is unknown, but presumably, it's to tie into the increased prominence of the orkish built-in ecology, and/or to give Feral Orks back their cavalry whilst distancing them from their Warhammer Fantasy (and now Warhammer: Age of Sigmar) counterparts. Their 'standard-issue' weapon is a spear called a Stikka - like their Imperial Rough Riders counterpart - except, instead of having an explosive tip, these Stikka have a rocket booster attached to its ass so when the Boy throws his shaft, its gonna fly and hit something from a distance with enough force to pierce power armour.
Other than that, they also have a trusty Grot saddlegit armed with "saddlegit weapons" such as a Squig Blasta that provide an extra attack at short range and in melee.
Nobz on Smasha Squigs
The biggest and strongest Squighog Boyz might even be able to tame and ride a mighty Smasha Squig. The Smasha Squig may not be quite as tusky as its pig-like counterparts, but it makes up for it by having a head like a battering ram and a desire to use it. The local Painboss seems to have upgraded the Smasha with a reinforced metal bonce, so that if it builds up a good head of steam, it can bash a sizeable dent into a Land Raider with its iron headbutt. With lighter infantry or vehicles, the Smasha Squig can sometimes bash its way all the way through and keep going, rampaging its way headfirst into the next enemy.
While the Smasha Squig enjoys the battlefield in its uniquely "cerebral" manner, the Nob riding on top wields a Big Choppa and a Slugga/Six-Shoota, taking swings and potshots at anything the squig hasn't already headbutted through a wall.
Krunch
On the tabletop, these are your primary Ork cavalry units. They are pretty durable (T6 and 3 Wounds each) and quite strong as well, and between the Ork's stikka and the squig's own jaws each model is a serious threat to MEQ equivalents, monsters, and vehicles alike. Even the saddlegit is able to provide some extra melee and dakka punch.
The Ork's stikka (which, as previously mentioned, is actually a rocket-assisted spear) can also be used as a ranged weapon that becomes a Gravis-wounding Strength 6 at 6" or less. It's Damage 2, so each unsaved jab is one dead Space Marine, and each Squig rider gets to dish out three attacks a turn with them! The whole mob can also be accompanied by a Bomb Squig for every three hogs, which is a really nice way to keep some mortal wounds in your back pocket for those clutch moments.
The Nob on Smasha Squig has reasonable killing ability with its Big Choppa and Squig Jaws, but the real reason you take them is to dish out an average of 2.5 (max 5) Mortal Wounds to anyone you charge or Heroically Intervene with: think of it as less of a single melee champion and more a forehead-based melee Smite that can be used to leave a big dent in anything with ridiculous saves/invulns, or even finish off a big durable enemy. If you get lucky and manage to finish off the entire unit on the charge. you can let the Smasha Squig charge again with the 1CP Unstoppable Momentum Stratagem, which lets it keep going and dishing out Mortal Wounds as a reward for trampling that last Custodes. The best part, however, is that for every unit of Squighog Boyz, you get to take not one, but TWO of these living battering rams in your army without taking up an Org slot!