GREETINGS I WOULD LIKE TO KNOW HOW YOU HAVE DEALT WITH TAU RIPTIDES SO FAR. IT SEEMS THAT ONCE THEY MANAGE TO GET THEIR 3+ INVULNERABLE THEY ARE PRETTY HARD TO KILL. THE FACT THEY CAN BE REPAIRED DOES NOT HELP.
GIVEN THE FACT THAT THEIR PERFORMANCE IS NOT INFLUANCED BY DAMAGE DUE TO SOME STRATAGEM I HAVE TO ASK WHAT IS YOUR STRATEGY IN DEALING WITH THEM (ESPECIALLY AGAINST AN ARMY OF MULTIPLE RIPTIDES)
THANKS IN ADVANCE FOR THE ADVICE.
ps (NOT DEALING WITH THEM MIGHT BE AN OPTION BUT IT IS NOT MY FIRST CHOICE).
You basicly want to force them to take a boatload of saves, easiest way to do that: high volume, high strength weapons. Preferably Basilisks and Manticores as you can hide them from (parts of) his army, but battlecannons and superheavies also do the trick. As a budget option Autocannons also work reasonably well against them; wound on a 4+, and deal two damage a shot. The riptide gets a 3+ armor save against them, but if you bring a bunch of autocannons (not all that hard to do) you can get a couple through and chip away at the riptides.
Psykers are another option: using smite and other powers to hit the riptide with mortal wounds.
Because it has the "fly" keyword you can't tarpit it, which would normally be an easy way to dealing with big scary shooty thing. But it also means that anti-air weaponry has an easier time hitting it, so hydra's are actually pretty good vs T'au (all vehicles and most suits have "fly") so it hits on a 3+.
You can also consider the "old grudges" warlord trait to make wounding a single riptide a bit easier, and tossing in some strategems to help out.
The reason most people choose to ignore riptides is because they are a pain in the behind to get rid off (but I suppose you noticed that), and whilst you dedicate your entire army's shooting phase to killing it.. the T'au player can position his other units to kill yours.
I haven't used my Tau since GW made the way I enjoyed playing them next to impossible.. so I'm not a 100% sure how they work this edition. But some things remain true in dealing with them:
- Indirect fire is your friend: all their scary shooting requires LoS, so if you can keep your scary stuff (Manticores, Basilisks) out of sight you have a big advantage in the shooting game.
- Kill the markerlights: drones and pathfinders are fairly soft targets, but they amplify the damage done in the shooting phase.
- Try and get into combat: most suits and vehicles can run away and still shoot, but infantry and broadsides can't. It'll also give him something to worry about as most Tau players are really worried about close combat. If you have a vehicle at half health in range of some firewarriors: charge them, preferably try and work in a multi-charge and screw with his gunline. The tank probably won't survive his shooting phase anyway, and as long as it is in combat he can't shoot it. When you are aggresively advancing units he is probably going to dedicate units to shooting those threats. Which in turn leaves your backfield units firing longer.
In short: the Riptide's nr.1 job is distraction, don't let him get away with it. Don't try and focus down a riptide at the expense of other threats, try and take out markerlights first, move up and get in his face with distractions of your own (hellhounds, sentinels, chimerea, etc.). And like a proper guardsman: get a bunch of artillery and blow him off the board.
Can't give you personal advice for the Imperial Guard, but there are some interesting ways Imperial allies can help. I have a Librarian as part of my Deathwatch detachment that has a spell to turn off invulnerable saves. it's 8+ so it doesn't always work, but the squad then can fire a WHOLE BUNCH of stuff, so even if it's not turned off, if you direct your entire army at it, it should go down. With Imperial Guard only, you will need to hit it with multiple high strength multi wound, multi damage things, and hope you get lucky
Manticores, Basilisks, Battle Cannons, a volley from several Vendettas might do the trick, as they are all high wound things. If he fails 1 save, it's not just 1 wound, he'd be taking a d6 from a lascannon. If you can manage to fit a unit in your army that can turn the invuln save off, it's freakin' cake from there
I once managed to kill a riptide with FRF, SRF on a unit of Conscripts, but this was back in 6th edition. Conscripts ain't so good at taking orders now, but basically, it was 150 shots. Hit on 2s, wound on 6s, but it worked. Might try that with some regular guardsmen, if you can get close enough
TLDR: Volume of shot, volume of wounds. Drown it in missiles and laser fire, it's the only way