The first thing that comes to mind here is that having a Dry Skin/Water Absorb Pokémon in OU immediately makes Scald a less spammable move. The Pokémon that are affected by this the most are, of course, Bulky Waters, but more specifically, Pokémon like Specs Keldeo and Suicune are disadvantaged the most because Esca's very presence on the other side of the field makes them far harder, or even impossible, to use. That said, I'm not sure that Dry Skin Escavalier will be that metagame-defining; after having a look at the VR thread, I can count seven Water-type Pokémon in A- and above (counting Gyarados and it's mega as separate Pokémon). Here's a list so you don't have to check as well:
Azumarill
Greninja
Gyarados
M-Gyarados
Keldeo
Manaphy
Rotom-W
252+ Atk Escavalier Iron Head vs. 252 HP / 0 Def Azumarill: 178-210 (44 - 51.9%) -- 12.5% chance to 2HKO
Against Azumarill, Escavalier walls most of it's moves, but can't really hit it back. Azumarill is able to Belly Drum up in Esca's face while it can't do more that about 50% back, meaning that it can't kill Azu after the Sitrus Berry regen. After that,
+6 252+ Atk Huge Power Azumarill Play Rough vs. 252 HP / 0 Def Escavalier: 342-402 (99.4 - 116.8%) -- 93.8% chance to OHKO
In short, it's setup bait. Of course, Azu is left about about 25% of it's health, meaning that it's easy enough to take out, but it's still a terrible check to BellyJet.
Escavalier is a hard counter to Greninja, however, if it doesn't run Hidden Power [Fire]. The standard set fails to 3HKO with Dark Pulse, after which Esca can simply Megahorn it to death. Even if it picks a move that makes it neutral to Megahorn, it still OHKOs. It can U-Turn out, and Megahorn is a risky move when couple with Dark Pulse's 20% chance to flinch, but that's not something a Greninja user can rely on. Escavalier could do this before it received Dry Skin, however, as even without it Hydro Pump is still a 3HKO. The new ability just makes it easier to come in. One has to scout for Hidden Power, though.
Gyarados is a tricky one: an un-mega evolved MGyarados walls all of Esca's moves all day, as Knock Off doesn't remove it's item and it resists or is immune to everything else Esca commonly carries. This means that it can simply use Escavalier as setup bait, and if it decides to stay in:
+2 252+ Atk Mold Breaker Mega Gyarados Waterfall vs. 252 HP / 0 Def Escavalier: 313-370 (90.9 - 107.5%) -- guaranteed OHKO after Stealth Rock
If it's not a mega, however, Gyarados can boost up on it but has to take repeated Knock Off punishment, meaning that non-RestTalk variants lose:
(assuming Esca switched in on Gyarados)
252+ Atk Escavalier Knock Off (97.5 BP) vs. 4 HP / 0 Def Gyarados: 146-172 (43.9 - 51.8%) -- guaranteed 3HKO after Leftovers recovery
252+ Atk Escavalier Knock Off vs. 4 HP / 0 Def Gyarados: 97-115 (29.2 - 34.6%) -- 7% chance to 3HKO
Keldeo is another difficult one to deal with if you're facing a clever player. The only move it can use to hurt Escavalier is Secret Sword, and while it does sting (252 SpA Choice Specs Keldeo Secret Sword vs. 252 HP / 0 Def Escavalier: 199-235 (57.8 - 68.3%)), Esca takes little from it's other moves, and discourages it from spamming it's Water moves mindlessly, making it easier to set up in Keldeo's face with unlikely Pokémon such as SubTox Aegislash and SD Talonflame. Escavalier has a lot of influence against Keldeo, as the presence of Dry Skin causes all sorts of interesting mindgames. This one is still dicey, though.
Manaphy is hard walled. Not much to say here, so have some more calcs:
+6 252 SpA Manaphy Ice Beam vs. 252 HP / 4 SpD Assault Vest Escavalier: 104-123 (30.2 - 35.7%) -- 36.6% chance to 3HKO
252+ Atk Escavalier Megahorn vs. 0 HP / 0 Def Manaphy: 220-261 (64.5 - 76.5%) -- guaranteed 2HKO after Leftovers recovery
Again, if Escavalier becomes a major contender it may begin to run Hidden Power [Fire].
Rotom is not countered by Escavalier, at all. While it can switch in on Hydro Pump, washing machine outspeeds and can Volt Switch away or just burn it, and then Volt Switch away.
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So out of seven Water-types in A- and above, it hard-counters Manaphy and Greninja, but performs poorly against the other five. That said, however, on top of Manaphy and Greninja it also acts as a great answer to Tyranitar, Bisharp (with Drill Run), MVenusaur, Suicune, Lati@s that lack HP [Fire] and Kyu-B, among others. On the flipside, it's either wrecked or setup on by all of S-rank (Aegislash can simply King's Shield against anything it carries and force it out, with minimal repercussions should it switch immediately), and the prevalence of Heatran, Talonflame and the Charizard bros alone make it necessary to play conservatively with Esca. All in all, I'm not convinced that an immunity to Water-type attacks is enough to earn it a place in top-tier OU, but, to use the viability rankings, I would place it at around B.