Why does smogon recommend crunch over waterfall for Gyarados in it's Mega DD set?

Question

Just out of curiosity, why is this? When you look at Gyarados' smogon page, the mega dd set has crunch, earthquake, dragon dance and substitute with ice fang or waterfall as an option to replace sub. So what's the reason for this? I mean, when you use Mega Gyarados, timing is one of the things you need to think about and before mega evolving, crunch doesn't have stab. So, shouldn't this mean that waterfall would be the preferred stab?

Comments

Did you said it doesn't get STAB on Crunch after Mega-Evolving? M-Gyarados is part Dark-type.

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@Swastik "and before mega evolving, crunch doesn't have stab"

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Oh. Sorry didn't understand that.

Answer 1

Coverage

According to the type coverage checker,

Dark/Ground:
0 No Effect
26 Not Very Effective
608 Normal Effectiveness
400 Super Effective

whereas

Water/Ground:
1 No Effect
117 Not Very Effective
582 Normal Effectiveness
334 Super Effective

and

Water/Dark:
0 No Effect
34 Not Very Effective
680 Normal Effectiveness
320 Super Effective

All of this is not counting the Water Immunity some Pokemon have due to their abilities (Water Absorb, Storm Drain), so the ratio is actually skewed further in Dark/Ground's favour. So in general, simply by the numbers, you're a lot more likely to hit more Pokemon for more damage with Crunch/Earthquake than Crunch/Waterfall or Waterfall/Earthquake.

Of course, there are some exceptions to this, and the most popular sets will be the ones that can counter the biggest threats, i.e. a Crunch/Waterfall set wouldn't be as effective in a meta where Greninja is super popular, whereas Earthquake wouldn't be favoured in a Grassy Terrain meta. It's a matter of what sort of opposition you might have to deal with, but whoever made the set probably took into consideration data from a lot of battles which suggested that Crunch/Earthquake would over many battles, be more effective than the other sets.

Comments

Interesting. Thanks. I'll have to try the crunch + earthquake sometime

Answer 2

The Smogon page already answers your question.

Crunch is a strong primary STAB move that gives Gyarados good neutral coverage and hits Psychic-types such as Mew, Latios, and Slowbro super effectively.

Waterfall is an option that hits Ground-types like Landorus-T for super effective damage and hits certain Dark-resistant Pokemon like Clefable for neutral damage.

source
So crunch is super effective against more threats, and most Pokemon with water weaknesses don't resist dark.

Comments

That's what confused me. As I mentioned, timing is one of the complications to use Mega Gyarados since it reverses most of the type effectiveness against it. Before mega evolving, Gyarados won't have any stab if it has crunch and earthquake so that's what I don't understand

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I guess you just have to mega evolve it before it attacks. Even if it knows waterfall, you should mega evolve before using waterfall so your attack stat is higher.

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Well, that's true but it's not gonna be like other mega pokemon where you just have to mindlessly tap the mega evolve button. Still a bit confusing since Mega Gyarados is one of those mind games pokemon due to difference in type effectiveness