My opponent and I both have Sudowoodo with "Roadblock"Ability in play. I use Hex Maniac on my turn to shut off "Roadblock", and then I play 5 Pokemon on my Bench. My opponent plays 5 Pokemon on their Bench during their turn. At the end of my opponent's turn, Hex Maniac's effect ends, so "Roadblock" activates again. Who discards their Pokemon first? If the first player discards their Sudowoodo, would the other person need to discard a Benched Pokemon?

It's the opponent's turn, so their Roadblock goes into effect first. You would discard your Pokemon first, and then your opponent would discard theirs. Even if you chose to discard your Sudowoodo, your opponent would have to discard down to 4 Benched Pokémon because the Roadblock effects happen simultaneously.

Relevant cards

SMA_SV20