So it is that playing against Orks is always fun because all of the nasty things you wish to do to them work! In a universe full of Stratagems like the Dark Eldar have which simply switch off your "special stratagem combo", or Toughness values so great that you are cheering when you drop a mere three models in their tracks, orks provide the playground upon which any army can feel really good about their results. You have fun absolutely raking endless numbers with your flame, cannon and axe.
The Orks on the other hand are enjoying themselves. They get to move lots of stuff around and roll a ton of dice! When they reach you, they overwhelm their target. It feels good to sense your inevitable victory over the 'Umies even as Ork parts pile up also. Sure, you just lost 8 Orks in one salvo, 3 on Overwatch and 7 in close combat but so what...you're Orks, and there's more where that came from! Ask any non ork about how they feel when they pick up 15 models. The sadness in their eyes tells you all you need to know about why it's great to be an ork! Wanton and callous disregard for the lives of your Orks is empowering. Moreover, the Ork player has some silly tricks like mobbing up and you can almost never get an Ork down. There's just too much fighting going on. The Ork player is blessed with visually humorous figures and psychologically rewarding point prices for them, so that no particular loss feels soul crushing.
Orks are just fun.
And now, they are dangerous. Very very dangerous.
The tournament I attended a couple of weekends ago featured Orks at 1st and 2nd place. What was more telling than that however is who played them. Of the two, one was essentially new to Orks and had obviously cobbled together Orks from various friends just to play them. Three Dakka Jets, 90 orks, 25 Lootaz, some characters and some Gretchin. Sounds simple because it is and its similar to what I play, if not for the Jets. His first time with Orks in a tournament and I'll be darned if he didn't go ahead and win it all.
Someone brand new picked up the Codex and won with it. In a competitive meta. That happened.
A Few of the Dirtiest Ork Triks
The Mob Up ability was very good to begin with in the Index when it dropped, allowing 40 man Boyz squads to be shot-put'd towards the enemy with enough wounds to weather the nasty leadership hit they inevitably would be forced to take. After all, 6+ saves aren't all they are cracked up to be. On its own this would have been a great reason to celebrate.
This can also be used on a unit if 15 and unit of 10 Lootaz. In turn, those 25 Lootaz can use a Stratagem that makes them get extra hit rolls on 5's or 6's. Which is quite deadly when they are Bad Moons who re-roll 1's... And that wouldn't be AS bad as it is if it weren't for the fact that the roll for the number of shots from the Deffguns now affects not 15 but 25 of them simultaneously...
It's awesome. you can almost take an Imperial Knight down with it, in one go. A little luck and he will go down.
Another fun trick for Orks is Gretchen. We have always seen them in our minds eye as bullet shielding. Lets be honest, they aren't good at much else and they scamper away into the weeds at the very first sign of trouble. Sitting on an objective completely out of sight like the cowards they are is their best suit and at it, no one does it better but such an ignominious fate...
Now when an enemy selects the aforementioned Lootaz as a target to shut them up, the gretchen can pop their Stratagem to LITERALLY throw themselves in front of the bullets. If they are closer to the enemy than the Lootaz are, the Gretchen can now take the hits for the Lootaz. This is absolutely terrifying when you really think about it. It guarantees that the Lootaz will be firing 2-3 times a game unless you have some way to wrap them up into melee and hook oneof the models with your consolidation! Every gretchen within 6" must now take it to the face for their overlords in all their exploding glory.
This changes how you must deal with orks. Suddenly your only choice is to all your weakest firepower, dedicated to flushing Gretchen down the toilet before you can fire at the Lootaz or option B, once they pop the Stratagem, is to select a different target. but if you do that you're DEFINITELY in danger of not killing the Lootaz ever again. Powerful Catch-22.
More ork Dirty Triks? Well this happened to me in my game against the eventual winner: I tore his unit to ribbons, and he popped a one use only Stratagem, 3 CP and took the remnants off the board, and brought it back full strength within 9" at the end of the movement. And then charged the unit I had spent so much time unentangling. I mean they can re-roll charges so it's a fair bet they willl make it and it really changed the game. He gained about 21 orks doing this net, but much more importantly was the fact that he had positional dominance because of it.
Da' Jump is the obvious go-to in the ork codex and it was in the Index. Moving 30 orks to within 9" with the ability to charge you? Ruh-roh! I don't think i need to tell you why that's bad. The REAL trick to this however is making sure the enemy can get their Warboss, Waaaagh Banner bearer (re-roll magic), Wierdboys (extra attack) and Painboy (Feel No Pain) into position. If they do manage to trail their boyz back to these fellows, the few orks it takes will never be missed as they bury you in ultra effective attacks that almost nothing can hope to survive. They may try to do it with 40 Boyz by mobbing up which makes this even more true. I'd highly recommend bringing 40 because T'au Empire T'au Sept overwatch and other factors can make the orks explode even if they are successful and have taken some casualties before jumping.
What to do
Well clearly when you build your list you must have a way to engage the Lootaz. Like all orks they melt like butter to real assault units with a good number of attacks (Sisters Repentia with Uriah, Death Company, or even Kroot Hounds if they can get there) and when you kill a Loota, you are killing a lot of firepower and a goodly sum of points as Orks go. So having a melee element, even for shooting armies, that can reach out and reliably reach Lootaz is important. it's very likely that units like this will become a staple of competitive armies so you better get used to it.
Once in the game, the other thing is to decide how much you need them dead turn one. If you can position so that you limit their damage to a dead rhino or something less important, then wipe out sections of Gretchen. It not only gives you space to deep strike but also forces as many morale checks on the Gretchen as possible. It doesn't take many casualties to pop a whole lot more of them. Riddle the various units with normal shooting if you can afford to.
Make sure something halfway decent aims at the Lootaz just to make him spend the 3 CP. If you don't fire ANYTHING at the Lootaz first, he won't be out the CP, which is advantage him. Consider it a feint, act like you wanna hit his Lootaz and then spray at those Gretchen all day long until they all have to take morale tests if you can pull it off. You don't need to kill whole units because morale will do the rest.
I suppose it might be obvious but if you can get a Psyker close, fast, that would also help. being able to deny Da' Jump power is really a big deal. I was fortunate in that I was playing Sisters of Battle and I never let him get Da' Jump off, even once. Our game was fairly close and I was making serious headway before they called dice down (orks are so slow!). However I think i would have done worse had he gotten that off and thoroughly boxed me in. Even without that he dominated objectives but stopping that is key. A Jump Psyker or someone who can get within 24" would be a really good idea in a lot of lists, or any items that allows you to do it. Just note where his specific Wierdboy with that power is and line up a Psyker diametrically opposite of him. Just stopping it once is a big deal. Unsupported and left as the only necessary target, ork hordes can melt without compensation for their efforts. But when they are coming from all sides? It's not good.
If you want to mitigate Da' Jump somewhat and IF you have the opportunity consider this advice: you will usually be able to tell WHICH ork unit will be the likely one to receive Da' Jump. The other two will likely be as far forward as possible while the likely candidate will not necessarily be. Shooting the Lootaz (other than to get him to spend CP) might seem like a waste given your deployment etc... But the unit that will use Da' Jump? PERHAPS you can sucker him into protecting IT with Gretchen and then let loose on the Lootaz if you go first turn 1! if he doesn't bite that's okay. If he goes first and you can blast and shoot up that Ork Boyz unit, then Overwatch it when it re-rolls its charges into you and THEN fight it, you might be able to force morale on it. If you kill 19 they auto-explode on Morale, forcing yet more Command Point expenditure from the enemy which is good because a lot of their most devastating triks are high CP cost and if you can drain them through target priority that is not a bad idea.
So to kind of summarize the tactics here: Deploy as far back as you can to make his Ork charges a bridge too far. Screen with whatever screening units you want, to sacrifice to the initial Ork forces. Target Lootaz with something decent to get him coughing up command points, then lay into his Da Jump unit. TRY to only kill it down to 11 orks so it will explode on morale or force more Command Points spent to save it. Often this will work because the other two units are surging at maximum speed and aren't thinking about having to bolster the courage of their buddies behind them Consider that if the unit is too large (over 10) he cannot "remove and recycle" them with the Stratagem I mentioned earlier! He just has to accept his losses. You can't stop them from Mobbing up if they took an extra 10 orks, but it's still solid to try this and take away those precious Command points that fuel so much of what the Orks can now do. Then kill the Gretchen units to force more morale explosions and leaving less Gretchen shielding (and since he'll likely try to save a more important unit than Gretchen, overloading them with morale checks ensures it) One last point on this gretchen item: shooting the Lootaz on the hopes that a stray shot will get through the gretchen shields might at first seem like a worthwhile thing to do, because there is a chance that stray shots could get through (on a roll of a 1+). It's a trap. The fact is that if you do this you are now trying to wound T4 instead of T2. So for all kinds of math reasons, once he pays the points for the Gretchen shielding, just shoot the Gretchen directly. I know it stings but if you can morale wipe a whole bunch more units this way it will be worth it since you probably aren't stopping his second barrage anyways. Kill what you can, when you can. Don't ride uphill to do it. In ITC formats, killing more units per round is a thing. This plays to that scoring system as well. You'remaking lots of kills early and you're making future kills a whole lot less work.
Well that's all for now. Just some random thoughts I felt like writing down for you. Use them or lose them.