If one of my Pokemon was knocked out by an effect of an attack or an Ability, would I still be able to play Letter of Encouragement?
Yes, there is no restriction on how the Pokemon was Knocked Out. However, a KO during Pokemon Checkup such as from Poison or Burn would not count.
Source: Obsidian Flames FAQ; TPCi Rules Team (2023-08-10)
Do I include Brassius in the count of my hand?
No, by the time you are counting the cards in your hand Brassius is already in play; it is no longer in your hand.
Source: Obsidian Flames FAQ; TPCi Rules Team (2023-08-10)
If my Active Pokemon was attacked by Tsareena's "Queenly Heel" attack, can I evolve it if I switch or retreat?
Yes, going to the Bench removes the attack effect so you can evolve what was your Active Pokemon, and also your new Active Pokemon, if they are normally able to evolve.
Source: Obsidian Flames FAQ; TPCi Rules Team (2023-08-10)
If I use Ninetales' "Nine-Tailed Dance" attack which Pokemon can't attack next turn, Ninetales or the Pokemon that was attacked?
Ninetales can't attack.
Source: Obsidian Flames FAQ; TPCi Rules Team (2023-08-10)
If I use Houndstone ex's "Last Respects" attack, would I count each piece of Mewtwo V-UNION in my discard pile as a separate Pokemon?
Yes, each piece will add to the damage.
Source: Obsidian Flames FAQ; TPCi Rules Team (2023-08-10)
If I use Seismitoad's "Echoed Voice" attack three turns in a row, would I do 320 damage on the third turn?
No, the bonus damage doesn't keep stacking. It is only applied for each next turn, so you would do 120, 220, 220, etc.
Source: Obsidian Flames FAQ; TPCi Rules Team (2023-08-10)
If I use Lampent's "Alluring Fireball" attack or Elektross' "Suction Shock" attack and my opponent has no Benched Pokemon, do I do damage to or get to flip to paralyze the current Active?
No. The attack specifies that the damage and effect are only done to "the new Active Pokemon"
Source: Obsidian Flames FAQ; TPCi Rules Team (2023-08-10)
If Pokemon League Headquarters is in play and I have Lunatone with the "New Moon" Ability and also Solrock in play, do my Basic Pokemon have an extra {C} cost to their Attacks?
No, but your opponent's Pokemon do.
Source: Obsidian Flames FAQ; TPCi Rules Team (2023-08-10)
If I have both a Lucky Energy and a Gift Energy attached, what happens to a Pokemon if it receives enough damage to be knocked out? Do I get to choose the order of effects, or does one happen before the other.
You do not get to choose the order of effects. Lucky Energy's effect happens when damage is placed onto the Pokemon. Then Gift Energy's effect happens later when checking to see if the Pokemon is KO'd or not.
Source: TPCi Rules Team (2023-07-13)
What happens if I play Worker and cannot draw any cards? Do I still get to discard a Stadium or not?
Yes, they are two separate sentences so you do as much of it as you can.
Source: TPCi Rules Team (2023-07-13)