1. While we're here, how would the game know I want to use gen 1 clefable and not gen 9 clefable.
2. That's nice to know, but I also wonder if you're able to dynamax and terastalize different pokemon in the same game.
3. How would conditions that changed across generations work? Say a gen 9 dragapult burned a gen 2 Tauros. Would Tauros take 1/8th of its Max HP per turn (like in gens 2-7) or 1/16th of its Max HP (as burn works currently).
1.Because both Clefable (RB and SV) will be available in the Pokémon selection when you choose the Anygen Goes format.
2.Anygen Goes is closer to Anything Goes than Pure Hackmon, so only a SS Clefable can Dynamax, just as only an SV Clefable can Terastalize; in short, a version of Clefable (which is becoming the mascot of the format lol) will only be able to do what it could do exclusively within the of their own generation.
3.The consequence of any effect takes precedence over who causes the effect in this format, so yes, RB Tauros will lose HP from burn just like in the 1st generation, regardless of whether the Pokémon that caused the burn is from the current generation.
To complement what I said (consequence >>>>>> cause) applies to everything; Imagine this scenario: your RB Tauros faces the opponent's SV Tauros:
Turn 1: The opponent's Tauros attacks first because it's holding a Choice Scarf (since your Tauros can't hold any items). They use Body Slam hoping to paralyze your Tauros, but they don't know that Generation 1 Normal-Types are immune to paralysis caused by secondary move effects. You then use Body Slam against the opponent's Tauros, and the paralysis works because current Normal-Types don't have the immunity your Tauros possesses.
Turn 2: The opponent's Tauros has lost speed due to paralysis, and now your Tauros attacks first. You expect to finish this battle with Hyper Beam because A) Hyper Beam in Generation 1 used ATK and B) You know there's a good chance of a critical hit because Tauros's SPE is high, and the chance of a critical hit increased the faster the Pokémon was in Generation 1; but the opponent's SV Tauros turns Steel-type and resists your powerful Hyper Beam. However, the damage the SV Tauros took (even after turning Steel-type) was high because A) The damage received was critical and B) Hyper Beam calculated the RB Tauros's ATK against the SV Tauros's SPD, since Hyper Beam is a physical move for RB Tauros, while the same move is special for SV Tauros, which had to defend with its SPD, not its DEF (remember: consequence >>>>>>> cause).
We also haven't talked about items; they work like moves and special mechanics, meaning a Pokémon from any generation can only use items that existed in its generation. And since we're imagining a battle between Tauros from different generations, how about using a Tauros holding a Berserk Gene? Well, choose a GS Tauros : )
Finally (but let's keep talking), I imagine this metagame could be a lot of fun. I can even imagine the forum discussing the Anygen Goes tiers (will GS Snorlax be OU? That would be interesting to see)!