Single Strike Energy - Impact Energy

HatsWearCats

Impact Energy isn't considered a Single Strike Energy for Houndooms ability, or for Urn of Vitality. So it can't be searched and attached by Houndoom, or returned to deck with Urn

This has been a bug for at least a month

TechHog

That's not a bug. Both of those cards specifically say "Single Strike Energy," and thus can only interact with the card named exactly "Single Strike Energy." It is slightly confusing, but that's the official ruling. If they said "a Single Strike energy card" they would work the way you think, but this is not the case.

TechHog

Since I can't edit, I need to add that the last line is wrong. Basically, since there's a card named "Single Strike Energy, that's all they can target.