Can I use "Teammates" if my Pokemon was KO'd due to Poison damage?
No, you cannot. You can only use Teammates if your Pokemon was KO'd *during* your opponent's last turn, but Poison damage takes place *in between* turns.
Source:
Primal Clash FAQ (2015-02-05), TPCi Rules Team (2015-02-05)
If I have an opponent's Pokemon Tool F card attached to my Pokemon-EX, does its effect stop working if I evolve into Togekiss with the "Bright Veil" ability and make it my Active Pokemon?
Bright Veil only affects the play of an Item. That means the act of playing it. If it is already in play, enabling Bright Veil has no impact on it. It will stay in play and keep doing what it is doing.
If my opponent has Togekiss with the "Bright Veil" ability Active, does that prevent me from attaching Pokemon Tool F cards like Jamming Net or Head Ringer to their Pokemon?
No, Bright Veil does not prevent you from attaching the Pokemon Tool F card to your opponent.
When Dimension Valley is in play, if Mew EX uses its "Versatile" Ability to copy an attack from another Psychic Pokemon, will the attack's Energy cost be reduced by (CC)?
No. When Versatile copies the attack it uses the original attack cost regardless of the opponent's Pokemon's type, and then Dimension Valley reduces the cost by (C) since Mew EX is Psychic.
The wording of Jamming Net is now as follows, "The attacks of the Pokémon this card is attached to do 20 less damage to each of the opponent's Pokémon (before applying Weakness and Resistance). (Don't apply Weakness and Resistance for Benched Pokémon.)" This tool should only impact the Pokémon belonging to the opponent of the attacking Pokémon.
Source:
TPCi Announcement (2014-11-18), TPCi Rules Team (2014-11-20)
The wording of Fighting Stadium is now as follows, "The attacks of each {F} Pokémon in play (both yours and your opponent's) do 20 more damage to the opponent's Active Pokémon if it is a Pokémon-EX (before applying Weakness and Resistance)." This stadium should only impact the Active Pokémon-EX belonging to the opponent of the attacking Pokémon.
Source:
TPCi Announcement (2014-11-18), TPCi Rules Team (2014-11-20)