Ruling So many questions

[NIRVANA]

I have a dout, whats happen when I use Hippodown´s Lv. x Poke-power from DPT2?

Hippowdon LV.X - Fighting - HP130
Level-Up

Poke-Power: Sand Reset
You can use this Power once per game, during your turn. Each player returns all of his or her cards in play, other than Pokemon and Supporter cards, to his or her deck. Then, each player shuffles his or her deck. This Power can't be used if you already used another Sand Reset Poke-Power during this game.

he other dout is gallades Sw attack when I use sonic balde , when my opponents swithc If who chooses the new defending? Some cards like nidoking sw says for my opponent choose but when don`t say for opponents scoose I think I choose.

Sonic Blade
Put damage counters on the Defending Pokémon until it is 50HP away from being Knocked Out. If you do, the opponent switches the Defending Pokémon with 1 of his or her Benched Pokémon

And the last questions is If I have one Gardevoir Sw in My bench and one Unknown G attach, and My opponent atack me with manetric from DPt1 Gc, Can I prevent the damege? because the atck only do damage to pokemons with powers, bur I presume Is one effect.

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Manectric LV.45 – Lightning – HP90
Stage 1 – Evolves from Electrike

Poke-Body: Electric Barrier
Prevent all damage done to your Benched Pokemon (excluding any Manectric) by attacks.

[L] Power Wave: Does 30 damage to every Pokemon in play with any Poke-Powers.
[C][C] Induction: 40 damage. Search your deck for 1 Lightning Energy card and attach it to one of your Pokemon. Shuffle your deck afterward.

Weakness: Fighting (+20)
Resistance: Steel (-20)
Retreat: 0

 

[Blaine]

For Hippowdown I´m almost sure that it shuffles all cards in play (both of your and your opponent´s energies, tools, TM, Stadium and any other thing attached to your Pokemons (I´m not sure if there is something else, but it also shuffles Unowns) but Pokemons and Supporters (realize that the Discard Pile, the hand and the prizes aren´t in play) in the deck.
For Gallade the attack say "Your opponent switches the Defending Pokemon with 1 of his or her Benched Pokemons" so your opponent decides which benched Pokemon send to the Active position. Instead, if the attack said "Switch the Defending Pokemon with 1 of your opponent´s Benched Pokemon" you will be able to decide whinch Pokemon to swich.
For the last one, Unown G doesn´t prevent Power Wave as it say "Does 30 damage to every Pokemon in play with any Poke-Powers" and that is damage such as Kingdra´s Dragon Pump bench damage isn´t prevented by Unown G. If the attack said "Put 3 Damage Counters on every Pokemon in play with Poke-Powers" Unown G would be able to prevent it as placing damage counters is an effect of an attack when "30 damage" is damage.