I can see the utility in Strong Jaw, but I think some people don't quite understand the power of no recoil Head Smash. Heck, it makes Relicanth pretty decent.
In early DPPT there was a moment where normal Aggron almost made into OU just because he had CB Head Smash, which was capable of 2HKO on every single targets except like Hippowdon (although Aqua Tail hurted even Hippo). And we look into something with even higher base attack. To put it into perspective, Head Smash had the SAME base power as... water spout. Now imagine physical version of Specs Kyogre, with as good offensive STAB to work with and physical walls being weaker then special ones in Pokemon. And remember, there's nothing which matches the bulk of Blissey/Chansey when it goes to physical walling, so something ends up in the world of pain. Remember, this thing has BETTER typing and POWER behind their Head Smash then old Aggron. To put it into perspective... some damage calcs. All calcs are with Adamant Choice Band:
120 HP Conkeldurr (the bulkiest common Conkeldurr version)
52.49%-61.94%
Clean 2HKO. No chance to survive second hit.
Max HP/Max Def Positive Nature MegaScizor (base physical 70/140, which is great)
63.66%-75.00%
This is the bulkiest possible variant of MegaScizor, which I assure you won't run this many EVs anyway. Let's go with Max HP.
83.72%-98.55%
74.36% for OHKO with SR up. MegaScizor is considered one of the best checks to CB Tyranitar. Well, he certainly can't do the same in case of Tyrantum.
Maybe Gliscor ? Physically defensive version:
67.33%-79.55%
SubToxic
79.26%-93.18%
Ok, let's go with Standard Physical Wall Skarmory.
66.97%-78.90%
Good luck, no chance in hell to take on Head Smash.
Ok, maybe let's go with Tangrowth. Really, really physically bulky Pokemon. Oh well, let's see how he works. Of course standard OU Physical Wall Tangrowth.
58.81%-69.23%
Well no luck here as well.
Well, we still have Cresselia, right ? Well... yeah, we do. Max HP/Max Def version.
55.08%-65.01%
Or not. No chance for her as well, especially with SR up. Without it massive 1% chance to survive two hits counting Leftovers. Well, not the best odds.
Oh well, maybe let's try some resists. Ferrothorn must handle him like a boss ! Ok, let's see. I assume Standard OU set.
37.50%-44.32%
While you indeed survive two hits, those are pretty heavy. If Ferrothorn takes at least 20% of his HP earlier, he goes in two hits. Or you may just use Fire Fang:
87.50%-103.41%
Ok, maybe it's comeback time for Swampert ! Well... who knows. Max HP/Max Def Swampert.
36.91%-43.39%
Yeah, you survive two hits, but those are pretty heavy. The same situation as in case of Ferrothorn - you better don't take any damage before switching in or you'll be in a world of pain. BTW you don't have reliable recovery, so for your own good you better get good Wish support or run RestTalk. So technically you have ONE 100% safe switch. Although at 100% I admit that he counter everything Tyrantum can throw on him.
Well, in case of offense, we also need something that can switch on this guy. Terrakion for example:
64.51%-75.93%
Well yeah. I hardly call this reliable switch if you ask me. Yeah, you survive hit, but you only have one shot to do. And in case of Earthquake...
115.43%-135.80%
Ouch... Yeah, offensive teams may need something different. Like for example MegaMawile. Sounds good, right ? BTW this is Max HP/Max Def Positive Nature version.
38.82%-45.72%
Yeah, this is most physically bulky version. Let's go with more standard Max HP one.
51.97%-61.18%
Nope. No Leftovers to save your butt here, so 2 clean hits. Well, MegaMawile may end up unlucky though and switch on Earthquake...
92.76%-109.87%
While Aegislash (Shield Form) can indeed handle Head Smash (37,09%-43,68%), it doesn't stand a chance against Earthquake (65,93%-78,02%) though. Ok, there is always Eviolite Doublade.
24.93%-29.36%
Impressive. He takes this hit really damn well. Although lack of recovery hurts. Of course this is Max HP/Max Def version with Eviolite. Yay, we have a counter. Yeah... but Earthquake is not something you take with huge comfort.
44.32%-52.63%
17,03% for 2HKO. Well, in the end you may go in two hits. So it's hardly a counter. Great check though.
While physical Hippowdon is indeed 100% counter, in case of Specially Defensive I wouldn't be so sure. Although Slack Off helps. It still hurts though.
39.52%-46.67%
This is with Careful nature. For a resisted hit it hurts like hell. Well, Dragon Claw hurts him pretty hard though.
42.38%-50.00%
A little bit of passive damage (for example from Gengar which this version of Hippowdon is supposed to check) and he goes in two hits.
And to end this Jirachi. Few calcs:
Physically Defensive Wish + Calm Mind:
Earthquake =
61.39% - 72.77%
Head Smash=
34.65%-40.84%
Max HP Jirachi:
Head Smash =
47.52%-55.94%
Earthquake =
84.65%-100.00%
4 HP Jirachi:
Head Smash =
56.30%-66.28%
Earthquake =
100.29%-118.48%
In other words - If you run stall you better have Swampert, Physically Bulky Conkeldurr or Hippowdon with Positive Defense Nature (or physically bulky) if you look for 100% counter or you're screwed. CB Head Smash rip to shreds everything that doesn't resist his hits and good amount of resists as well. Head Smash + Earthquake is literally everything you need to 2HKO or OHKO pretty much all OU tier with those two moves alone (and I would say 80-90% of those happen with Head Smash anyway). More offensive teams if they'll allow this thing to switch it (with decent bulk and some good resistances he should find those free turns, especially with good support like VoltTurn) they will technically need to sacrifice something on switch, it hits THAT hard. And remember - no recoil, so you can't rely on recoil to wear this down. And taking into account that even bulkiest Rock resist take around 35-45% of their hp on switch, I wouldn't call constant switching the smartest idea to counter this. I would say this thing for slower teams is a nightmare unless they use hardcore rock resist. If they don't - oh well, I feel sorry for them. And they really should hope that Tyrantrum won't get Aqua Tail in future or it may look even more grimm...