pokemon 151 switch card (Gold) - SV: Switch your Active Pokémon with 1 of your Benched Pokémon 206/165 switch trainer card Pokémon

You can read all about it in Collecting Magic: The Gathering Doctor Who

If a player paid life for some other reason while casting the spell, that will not reduce the number of loyalty counters the planeswalker enters the battlefield with

Even if you couldnt activate Scavenge in response to itself, it would still be possible to return the card with Scavenge from your graveyard to your hand in response to the activation, allowing you to cast the card later or discard it to Scavenge again later

The value difference between shadowless and shadow bordered cards rises even higher in the case of "first edition" stamped cards