No, the effect is very much on Toxicroak G, because the Tool that is being discarded by the attack is attached to it, and therefore Pulse Barrier runs right into Anticipation. It is just like the ruling on Pachirisu's Smash Short. No attack in the game can pry Tools off Toxicroak G, just like no attack in the game can pry Unown G off a Pokemon. The effect is not on your opponent because you are doing the actions directly to their Pokemon.
If the opponent has any other Tools in play on other Pokemon (aside from benched Toxicroak Gs), or if they have a Stadium in play, then Electivire lv. X does get complete immunity during the opponent's next turn. Otherwise, the Tool stays on Toxicroak G and the attack simply does its 50 damage, with no effect.