It doesnt matter how exactly that happens: Sacrificing a creature is moving it from the battlefield into the graveyard
Let's look at some common threats that could affect your collection, leading to a reduction in your Pokemon cards value: 1
Previously, planeswalkers were subject to a planeswalker uniqueness rule that stopped a player from controlling two planeswalkers of the same planeswalker type
There are a few reasons why, but perhaps the most relevant is that there is a much better version of Pikachu, and you will want that out on the table if you can have it
That's the joy for them: gaining knowledge, applying that knowledge against worthy opponents, adapting, gaining new insights, and evaluating how to change their behavior to do better next time
Interested parties should not blindly follow the hype or the herd mentality, but rather do their own research and analysis before buying or selling any card or choosing product to invest in