Pachirisu's "Trick Sticker" attack says, "the Defending Pokemon's Weakness is now {L} until the end of your next turn". Does that mean the weakness is applied "now" before the damage is done for this attack?
Nice try, but no. Like all attacks that don't explicitly say otherwise, the effects of attacks are not applied until after damage is done.
Source: TPCi Rules Team (2015-05-07)
Say the "Sky Field" stadium is in play and I have 8 Pokemon on my Bench. My opponent uses Salamence's "Shatter" attack to KO my Active Pokemon and discard the stadium. Do I promote one of my Benched Pokemon first, or do I reduce my bench size to 5 Pokemon before promoting?
When the Sky Field stadium is discarded during the attack, the bench size is reduced immediately before going any farther. So after promoting your new Active Pokemon there will be 4 Pokemon on your Bench.
Source: TPCi Rules Team (2015-04-30)
If I use Beedrill's "Allergic Shock" attack, and then on the following turn I use an attack that does damage and the Defending Pokemon is KO'd, can the opponent add extra damage if they use an attack like "Revenge" or "Retaliate"?
If damage from your attack on the following turn is enough to KO the Pokemon, then the opponent would get to add extra damage for Revenge/Retaliate because their Pokemon was KO'd due to damage. But if there wasn't enough damage to KO the Pokemon and it gets KO'd due to the effect of Allergic Shock, then the opponent would NOT get to add extra damage for Revenge/Retaliate.
Source: TPCi Rules Team (2015-02-26)
For Milotic's "Aqua Swirl" attack who gets to choose which Benched Pokemon becomes the new Active Pokemon?
First off, since the attack says "you may" the attacking player gets to choose if any switching happens at all. Then if so, the opponent gets to choose which the Benched Pokemon becomes their new Active Pokemon.
Source: Primal Clash FAQ (2015-02-05), TPCi Rules Team (2015-02-05)
Does Sharpedo EX's "Hunt" attack do 30 damage if the opponent cannot switch their Active Pokemon to the Bench or if the Bench is empty?
If you cannot switch the opponent's Pokemon there is no "new Active Pokemon" to be damaged, so no damage is done.
Source: TPCi Rules Team (2015-02-05)
If I attack with Sceptile's "Power Poison" attack, do I have to discard an Energy card if I don't want to Poison the opponent's Pokemon?
It is not optional. Even if the damage would be enough to Knock Out the Pokemon, you still have to discard an Energy and Poison it.
Source: Primal Clash FAQ (2015-02-05), TPCi Rules Team (2015-02-05)
Can I use Mr. Mime's "Trick" Attack to move a Team Flare Tool card from a Pokemon-EX to a non EX Pokemon?
Yes, and it would immediately go to its owner's discard pile.
Source: Primal Clash FAQ (2015-02-05), TPCi Rules Team (2015-02-05)
What happens if M Gengar EX uses its "Phantom Gate" attack to copy Xerneas EX's "X Blast" attack? Can it use "Phantom Gate" again the following turn at all or not? Or would it just not be able to copy "X Blast" twice in a row?
The X Blast attack puts an effect on Gengar that prohibits using that particular attack next turn. But M Gengar EX is using its Phantom Gate attack on the following turn, so yes it is able to copy X Blast twice in a row.
Source: TPCi Rules Team (2015-01-22)
If my opponent KO's my Active "Robo Substitute", would I get the extra benefits from Terrakion's "Retaliate" Attack or Toxicroak's "Revenge" Attack?
Yes, you would. Even though Robo Substitute does not give up a prize card, it still counts as a KO'd Pokemon.
Source: TPCi Rules Team (2014-12-04)
If I use Kyogre EX's "Smash Turn" or Celebi EX's "Wind Whisk" or Gengar EX's "Dark Corridor" attack, can I switch it with my benched Sigilyph that has the "Safeguard" Ability?
Since the attacking Pokemon is the target of the switch effect, Sigilyph can be moved in this situation.
Source: TPCi Rules Team (2013-01-31), TPCi Rules Team (2014-11-13)