There are two insanely useful mons from past gens. Crawdnaut and Amoonguss.
Crawdnaut is probably best and most versitale wallbreaker. I even think that it outclasses hoopa with it's ability to break through defensive cores. Lots of mons are giving now free turns (celesteela, ferrothron, toxapex, tapu fini and others) with protect and things like that giving opportunity to set up SD. It has just enough speed to hit all those annoying walls like rotom or lanod-t. And most important: +2 knock off deals massive damage to venusaur!
Yeah except definitely not lol. Outside of Landorus there is nothing in the tier that compares to Hoopa-U's wallbreaking and hole punching capabilities. Crawdaunt is very strong and has priority sure, but Hoopa-U has an expansive movepool that covers practically anything relevant, insane offenses which lets it run mixed, physical, or special sets, and Dark Pulse/Hyperspace Fury are among the most spammable moves in the tier, even more than Knock Off considering that Megas and itemless mons have a potential to play around it. Hoopa also has great special bulk which lets it soft check a lot of special attackers and fire off hits, something Crawdaunt can't do due to its terrible bulk. Its Speed tier is also great for a wallbreaker, 80 compared to 55 is quite significant, and gives it the jump on every defensive threat + a few offensive Pokemon. Crawdaunt isn't versatile at all, in fact it's very linear considering it's always going to be running Jet, Knock, Crabhammer, and either SD or Crunch depending on if it's Band. Everyone knows what it's going to do, which is fine considering how dangerous it is, but Hoopa has the advantage of having so many move variations that it's not that easy to scout and by the time you do you've probably already lost a mon.
Crawdaunt is no doubt a cool Pokemon still, but it's definitely not anywhere near the level of Hoopa-U, and saying that it outclasses it is a huge over exaggeration. In fact, Crawdaunt is definitely not as useful as it was in ORAS because of the massive amounts of better breakers out there, and on top of that it has to worry about a few more checks/counters that it didn't really have before, particularly Koko, Fini, and Bulu, and the massive influx of Mega Venusaur/Mega Gyarados doesn't help it much either.
Amoonguss on the other hand is bulky mon that can fit into offensive teams. It gives amazing utility with clear somg (this is wining me game after game) which deals with porygons-z, z-rain dance manaphy (overrated set), CM tapu fini and others. It walls tapu koko, tapu bulu and tapu fini. Amazing mon!
Wait what are you smoking exactly? How is Z Rain Dance Manaphy an overrated set when that's like the only set you should really be running these days anyway lol. Tail Glow 3 attacks still has its merits I guess, but Z Rain Dance fixes the major problem that Manaphy usually has, which is actually threatening offense. Not only can Manaphy STILL break through stall and fat teams, but now it has the decision to late game sweep at +1 or just blow something completely out of the water (lol) with an extremely powerful Water-type move, doing insane amounts to even the fattest of walls. This set is what makes Manaphy so good right now, otherwise it wouldn't be nearly as insane as it is now. Z Rain Dance pushes it from a high A- Pokemon to like top A+ easily.
