Intelligence: High (Has a higher weakness to the Dragon Element than the average hunter: Deviljho has -15% resistance, while the average hunter has 0% resistance, and despite being mostly driven by hunger and rage, it can specifically choose its prey)
I do not even understand this justification. At least, not the first part; What does an Elemental Weakness have to do with its Intelligence?
What is a Deviljiho's typical behaviour in combat?
As for Tyranitar's....
| Gold | Its body can’t be harmed by any sort of attack, so it is very eager to make challenges against enemies. |
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| Silver | Extremely strong, it can change the landscape. It has an insolent nature that makes it not care about others. |
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Ruby
Sapphire | TYRANITAR is so overwhelmingly powerful, it can bring down a whole mountain to make its nest. This POKéMON wanders about in mountains seeking new opponents to fight. |
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| Ultra Moon | This Pokémon is a mobile disaster, leaving mountains crumbled and houses destroyed in its wake. |
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| Shield | The quakes caused when it walks make even great mountains crumble and change the surrounding terrain. |
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Brilliant Diamond
Shining Pearl | If it rampages, it knocks down mountains and buries rivers. Maps must be redrawn afterward. |
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But this is the 6-C Key, which means it's Mega Tyranitar.
| Ultra Sun | Due to the colossal power poured into it, this Pokémon’s back split right open. Its destructive instincts are the only thing keeping it moving. |
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| Ultra Moon | The effects of Mega Evolution make it more ferocious than ever. It’s unclear whether it can even hear its Trainer’s orders. |
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So uhhh yeah.
SBA still says they begin aware of one another & already intent on fighting, right? Because if so, we can forget the "wander looking for opponents to fight" part, it's just straight up going to "challenge"/attack Deviljiho, AFAIK, probably being very inconsiderate & destructive.
Because of Tyranitar's Sand Stream Ability, it will cause a Sandstorm immediately. Aside from residual damage & perhaps an obscured field of view for Deviljiho if it's not immune, in gameplay, Sandstorm gives Rock types a 50% Sp. Def boost. Assuming that applies here, Tyranitar would be 50% more durable against non-Physical/"Special" attacks than its unmodified (Mega) Durability.
Based on behaviour, I'd speculate that likely moves (Level-Up) include Stomping Tantrum, Earthquake, Stone Edge, Rock Slide, Rock Throw, Screech, Thrash, & Hyper Beam.
Maybe Scary Face, Leer, &/or its biting moves &/or Tackle?
I assume those moves because Mega Tyranitar is implied to be operating on nothing BUT destructive instinct. Arguably, it could be implied it'd faint or such if not for them, especially depending on the implications of its back being split open.
Egg Moves are probably stuff like Pursuit, Stomp, Outrage, & Iron Head.
It does have options like Iron Defense, Dragon Dance, Focus Energy, Ancient Power & more, but again, destructive instincts, & when it rampages, it reshapes the landscape, so presumably, it'd be using landscape-reshaping moves here, not these moves that are less destructive &/or require more focus/thought.
Since it's noted as making quakes when it walks, Stomp, Stomping Tantrum & Earthquake might be especially likely, perhaps passively.
Part of me wonders if the biggest threat isn't going to be the environment; Is it a plausible risk for either side that Tyranitar just ends up opening a fissure (Yes, I know it doesn't get that move.) into the core of the Earth at some point or such?