After using Clefairy's "Moon-Watching Party" Ability, if I switch or retreat for a benched Clefairy can I use its "Moon-Watching Party" Ability too?
Moon-Watching Party can be used by multiple different Clefairy if you get them into the Active Spot. However, if you bring up a Clefairy that has already used its Moon-Watching Party Ability this turn, it cannot use it a second time.
Source:
Lost Origin FAQ; TPCi Rules Team (2022-09-08)
If I use Parasect's "Lethargy Spore" Ability after a Pokemon has been attacked by Dustox's "Nadir Powder", how many counters are placed on the poisoned Pokemon during Pokemon checkup?
Lethargy Spore resets any specific number of damage counters for Poison to 1, therefore overriding Nadir Powder's effect of 8 damage counters for Poison.
Source:
Lost Origin FAQ; TPCi Rules Team (2022-09-08)
If I use Drapion VSTAR's "Hazard Star" VSTAR Ability to poison my opponent's Pokemon with 3 damage counters during Pokemon Checkup, and I have Radiant Hisuian Sneasler with the "Poison Peak" Ability in play, does my opponent put 3 or 5 damage counters on their poisoned Pokemon during checkup?
Five damage counters. Poison Peak adds 2 damage counters to whatever the current number of damage counters are being placed for poison.
Source:
Lost Origin FAQ; TPCi Rules Team (2022-09-08)
Do I use Radiant Venusaur's "Sunny Bloom" Ability before or after taking prize cards at the end of my turn?
Sunny Bloom is used at the end of your turn after attacking and checking for a KO but before Pokemon Checkup. So if your attack causes a KO, you would take Prize cards first, and then get to use Sunny Bloom.
If my Radiant Greninja has already used its "Concealed Cards" Ability during my turn but then goes out of play, if I bring it back into play can I use "Concealed Cards" again on the same turn?