Update (10:12 PM November 19, 2017): Poké Transporter now supports Pokémon Gold and Pokémon Silver.

Update (2:29 AM September 21, 2017): With Pokémon Gold and Silver slowly rolling out on the eShop, we’ve dug up our article on how stats are recalculated from the Virtual Console releases of the Pokémon Game Boy games. At the time of publishing, Poké Transporter has not been updated to support Gold or Silver, but this article has been updated to reflect changes from the recent 1.3 update. The information here will likely apply to the imminent Poké Transporter update coming soon, which will being support for the games.

Pokémon Bank and Poké Transporter’s new updates have been released, and with it the ability to transfer Pokémon from the first generation games Pokémon Red, Blue and Yellow (RBY). A future update will allow the transfer of Pokémon from Pokémon Gold and Silver (GS) as well. One point of interest was how this would be made possible, given that for instance the first generation games had only one Special stat, a different IV system and no Natures or Abilities.

Dataminers such as SciresM on Twitter have held unravel the mysteries behind the transfer process. One can even be manipulated in your favour!

IVs

Individual Values (IVs) are determined randomly. However, at least three stats will have a perfect value of 31. That means that every transferred Pokémon from RBY or GS will have three good stats at least! The exception is Mew, who gets at least five perfect IVs instead.

EVs

Effort Values (EVs) are set to zero.

Nature

Nature is an interesting aspect. Bank determines what the new Nature is based on the gained EXP of the Pokémon:

Nature = EXP % 25

% represents the ‘modulo’  operator, and gives you the remainder when dividing by the number following it. If EXP was, say “1001”, the equation becomes 1001 % 25 = 1, as dividing 1001 by 25 gives you a remainder of 1.

Each number corresponds to a Nature, which is listed below (assuming the same system is maintained). If you’re determined to get a good nature for your RBY Pokémon, you can give it some EXP to do just that!

Ability

Almost every Pokémon from RBY will gain its Hidden Ability. There are three exceptions; Mew, the Weezing line, and the Gengar line. This is because these Pokémon have no Hidden Ability.

This means that Machop will not have the No Guard Ability when transferred. No Guard Fissure Machamp can’t exist!

Is it Shiny?

This depends on the IVs (or determinant values – DVs) of the RBY Pokémon. If they have an Attack IV of 10, a Special IV of 10, a Speed IV of 10 and a particular Defense IV, it will be shiny. (Note that in RBY, IVs went from 0 to 15, not 0 to 31 as in modern Pokémon games).

The Defence IV may be 2, 3, 6, 7, 10, 11, 14 or 15 for the Pokémon to be given Shiny status.

Before Poké Transporter’s recent 1.3 update, this worked slightly differently for the RBY Pokémon compared to the second generation games (Pokémon Gold, Silver and Crystal – GSC). In that case, the Attack and Defense stats were swapped (that is, Defense IV of 10 and Attack IV of any of the above numbers). This was changed in version 1.3, presumably to reflect how the just-released Gold and Silver calculate shinyness.

So, if you know the IVs of your RBY Pokémon, you can tell beforehand if it will be shiny or not! And if it is shiny in Gold or Silver on Virtual Console, it will remain shiny.

Gender

Gender was completely random. Now it will depend on the species being transferred as well.

Mew and Missingno

Legitimate Mew (via a Japan or Europe event) can be transferred. Mew obtained via glitches in RBY sadly cannot.

Missingno and other glitch Pokémon (e.g. ‘M) cannot be transferred in their forms. If, however, ‘M is in the form of a Kangaskhan and has illegal moves removed (think Water Gun and Sky Attack), it can be transferred.

Edited by Jake.
Special thanks to monkeybard and HaxAras for additional contributions.

Source: Daily.pokecommunity