Gourgeist's "Pumpkin Bomb" attack says to "discard any number of Pokemon Tool cards from your Pokemon", but can I choose a different Pokemon other than Gourgeist for this attack?
The term "Pokemon" in the attack is plural, so you can choose any or all of your Pokemon and discard as many Tool cards as you like from them.
Source: Crimson Invasion FAQ (2017-10-20), TPCi Rules Team (2017-11-02)
In a single-elimination match that goes to time and is tied during the final game, if I add prizes to my opponent's field with Nihilego GX's "Symbiont GX" attack on my turn, do I win?
Yes. After regulation time (plus any additional turns) is completed, once you have fewer prizes remaining than your opponent, you win.
Source: TPCi Rules Team (2017-11-02)
In a Sudden Death game, if I add prizes to my opponent's field with Nihilego GX's "Symbiont GX" attack, is the game won by the next player to take a prize, or the first player to take their last prize?
A Sudden Death match is complete when a player has taken all of their prizes, regardless of whether there is more than one or not. So adding prizes in this scenario makes it more difficult for the opponent to win.
Source: TPCi Rules Team (2017-11-02)
If I have Florges with "Calming Aroma" in play my attacks cost one Fairy Energy less. So I think I can use Zygarde's "Core Enforcer" attack without a Fairy energy attached, but what about the part of the attack that says to discard one Dark and one Fairy energy from this Pokemon?
You do as much of the attack text as you can, which in your situation means simply discarding one Dark energy.
Source: TPCi Rules Team (2017-09-21)
If I have a Dark Energy, a Rainbow Energy, and a non-Fairy energy card attached to Zygarde, when I use Zygarde's "Core Enforcer" attack can I discard the Rainbow Energy first for the Darkness discard, and then without a Fairy energy attached I'm done?
No, since you have Rainbow satisfying the Fairy Energy condition you would have to discard both the Rainbow and the Dark Energy.
Source: TPCi Rules Team (2017-09-21)
Weavile's "Rule of Evil" attack does damage to each Pokemon that has an Ability. But if Garbodor's "Garbotoxin" Ability is activated would "Rule of Evil" only damage Garbodor?
That's right, because Garbotoxin says each Pokemon (except those with Garbotoxin) have no Abilities.
Source: TPCi Rules Team (2017-09-14)
Can I use Diancie's "Sparkling Wish" Attack to search your deck for an Evolution card even if you have no valid targets to evolve?
Yes, you can, but only because it is an attack. You do as much of the attack as you can, so you can search through your deck but nothing more.
Source: TPCi Rules Team (2017-08-31)
If I move Wimpod to the Active position and then evolve it into Golisopod GX, would I get the bonus damage from "First Impression"?
No. Wimpod is not the same Pokemon as Golisopod GX.
Source: Burning Shadows FAQ (2017-07-20), TPCi Rules Team (2017-08-03)
If I use Eelektrik's "Small Appetite" attack against a Pokemon with 90 HP but it has the "Bodybuilding Dumbbells" Pokemon Tool attached, do I do 50 damage or 0?
You do 0 damage. The HP from Bodybuilding Dumbbells counts toward the Pokemon's maximum HP, putting it out of range of the Small Appetite attack.
Source: Burning Shadows FAQ (2017-07-20), TPCi Rules Team (2017-08-03)
Can I use Diancie's "Sparkling Wish" attack to evolve a Pokemon that I just put into play this turn?
Yes, you can do that.
Source: Burning Shadows FAQ (2017-07-20), TPCi Rules Team (2017-08-03)