If I use Sudowoodo's "Watch and Learn" attack on the turn after my opponent's Mew EX used its "Versatile" Ability, can "Watch and Learn" copy the attack that Mew EX used?
If I have multiple Infernapes in play, does each of their "Flaming Fighter" Abilities add 6 more damage to my opponent's burned Pokemon in between turns?
No, Infernape's Flaming Fighter ability does not stack. You are simply placing 6 damage counters instead of 2, regardless of how many Infernapes are in play.
Source:
Ultra Prism FAQ (2018-01-19), TPCi Rules Team (2018-02-01)
Can I use Lunala GX's "Psychic Transfer" Ability to move a {P} energy back to where I got it from on the same turn? How about if I move it between the same two Pokemon several times in a row?
You have to advance the game state with your actions. If your Psychic Transfers are mindless, then you are not advancing the game state and it could result in a penalty.
Source:
Ultra Prism FAQ (2018-01-19), TPCi Rules Team (2018-02-01)
What happens if I have Miltank with the "Moomoo Malt" Ability and my opponent has Gengar with the "Gnawing Curse" Ability in play? Which Ability goes first? Or does it even matter?
The player that owns the affected Pokemon gets to choose the order that the two simultaneous Abilities are applied. However, keep in mind that you cannot go below zero damage done; for example, if you have 50 damage and you use Moomoo Malt first, you can't "go negative" and then have Gnawing Curse's counters simply disappear. Also remember, if you choose Gnawing Curse first and the damage counters put the Pokemon over its maximum HP you still get to use Moomoo Malt before checking for KO's.
If there are two Gengar in play with the "Gnawing Curse" Ability, how many damage counters would be applied if the opponent attached an energy card to one of their Pokemon?
They would place 4 damage counters on that Pokemon.
Source:
Crimson Invasion FAQ (2017-10-20), 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.
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.