for dual types, is there any difference b/t which type is primary?

[geozeldadude]

been reading through pokemon trivia, and noticed that bulbapedia has one page listing dual pokemon by their primary types. does that make any difference, or is it just that that maybe implies what the egg group is and what types of TMs it can learn? just curious.

[CATS]

The latter. For purposes of determining type effectiveness, Water/Rock is exactly the same as Rock/Water.

[dondon151]

The only instance in which it actually mattered was in gen 1 when type effectiveness messages were always displayed against the secondary typing.

[Smiley Jim]

It doesn't matter what the order the types of a dual-typed Pokemon are, gameplay wise. For example, Garchomp(a Dragon/Ground type)has the same weaknesses(gets raped by Ice Beam)and resistances(laughs at Thunderbolts and Stone Edges)as Flygon(who is Ground/Dragon), since they are technically the same type. Also, they can learn similar moves(both get EQ, Outrage, Flamethrower, and Stone Edge. The only difference is that Flygon gets U-Turn and Chomp gets Surf), so you can't argue movepools. And Ground/Rock gets raped by Surf/Grass Knot the exact same way as Rock/Ground.

[dondon151]

Oh, wait, I do recall another subtle difference. Due to how the damage formula floors numbers after every operation, the typing order does matter for attacks that are SE against the primary type and NVE against the secondary type.

Take, for example, a Water type attack against Rock/Water. Water does 2x to Rock and 0.5x to Water, so the damage is unchanged compared to if it were completely neutral. If you used a Water type attack against Water/Rock, Water does 0.5x to Water and 2x to Rock, which means that the attack can only do an even amount of HP in damage (because numbers are floored after applying 0.5x to the original damage).

[Gash]

Are saying water v rock/water = 1.5x damage and water v water/rock is still .5x damage?

[Lord_Brand]

On 12/3/2020 at 4:58 AM, Gash said:

Are saying water v rock/water = 1.5x damage and water v water/rock is still .5x damage?

No, it's more like this:

Water Gun deals 21 damage to a Rock/Water-type. Rock doubles that to 42, then Water halves it back down to 21.

Water Gun deals 21 damage to a Water/Rock-type. Water halves that down to 10.5, which is floored to 10, then Rock doubles it to 20.

Thus, Water Gun's damage against a Rock/Water-Type is unchanged, but against a Water/Rock type, it deals 1 less damage due to the halved number resulting in a decimal which is floored (i.e., reduced to the next lowest integer) before being doubled. If the attack would deal an even amount of damage anyway, the difference is moot, but in the case of odd numbers, there is a very slight, usually negligible difference.

Edited December 8, 2020 by Lord_Brand

[ZeManaphy]

If you are using a move like Conversion or Revelation Dance, the primary type is the type for those moves, so yes it matters in that case. Very niche examples though.