Say my opponent uses Trevenant & Dusknoir GX's "Pale Moon GX" attack on my Keldeo GX with "Pure Heart" while Power Plant stadium is in play. If I replace the Power Plant with another stadium during my next turn, does Keldeo GX get knocked out at the end of the turn or not?
If Keldeo GX remains the Active Pokemon it will be Knocked Out. Keldeo GX's Pure Heart Ability *prevents* effects, but it does not *remove* existing effects. If an attack like Pale Moon GX places an effect directly on Keldeo GX, that effect cannot be removed by reactivating Pure Heart; in other words, effects that are removed when returning to the Bench can't be removed by Pure Heart.
Source: TPCi Rules Team (2020-01-09), TPCi Rules Team (2020-02-06)
Does a player need to offer a cut when shuffling something other than their deck, such as when playing Marnie?
Yes. The purpose of a cut is to reduce the opportunity for cheating; that applies anytime a player is randomizing their cards.
Source: TPCi Rules Team (2020-02-06)
Say I have Keldeo GX already in play, and my opponent uses Latios GX's "Clear Vision GX" attack with Power Plant in play. If I play a different Stadium to get rid of Power Plant, can I use Keldeo-GX's "Resolute Blade GX" attack now?
Yes, you can. When Power Plant is removed Keldeo GX's Pure Heart Ability turns back on, and Keldeo GX is no longer hit by the global effect of Clear Vision GX. If an attack does not place an effect on Keldeo GX directly, like an attack that puts an effect that isn't removed when returning to the Bench, it can be removed by reactivating Pure Heart.
Source: TPCi Rules Team (2020-02-06)
Say Sky Field is in play and I have 8 Benched Pokemon, then I use Marshadow's "Resetting Hole" Ability. Do I discard Marshadow first and then discard down to 5 Benched Pokemon for the removal of Sky Field, or do I discard down to 5 Benched Pokemon first and then discard Marshadow?
The player who owns Marshadow can choose the order of discarding Benched Pokemon, either before or after the removal of Sky Field.
Source: TPCi Rules Team (2020-02-06)
Can I use Sitrus Berry to heal damage received from Poison/Burn in between turns?
No, you cannot. Sitrus Berry only works at the end of a turn.
Source: TPCi Rules Team (2020-02-06)
If an attack would KO a Pokemon, can you use Sitrus Berry to heal it first?
No. KO's have to be resolved before the end of the turn, and Sitrus Berry heals at the end of the turn after KO's have been evaluated.
Source: TPCi Rules Team (2020-02-06)
The wording of Quick Ball is now as follows, "You can play this card only if you discard another card from your hand. Search your deck for a Basic Pokémon, reveal it, and put it into your hand. Then, shuffle your deck."
Source: TPCi Announcement (2020-01-09), TPCi Rules Team (2020-01-09)
The wording of Hyper Potion is now as follows, "Heal 120 damage from 1 of your Pokémon that has at least 2 Energy attached. If you healed any damage in this way, discard 2 Energy from it."
Source: TPCi Announcement (2020-01-09), TPCi Rules Team (2020-01-09)
The wording of Lum Berry is now as follows, "At the end of each turn, if the Pokemon this card is attached to is affected by any Special Conditions, it recovers from all of them, and discard this card."
Source: TPCi Announcement (2020-01-09), TPCi Rules Team (2020-01-09)
The wording of Pal Pad is now as follows, "Shuffle up to 2 Supporter cards from your discard pile into your deck."
Source: TPCi Announcement (2020-01-09), TPCi Rules Team (2020-01-09)