Any time I discover a card with Pichu in its artwork which I didn’t know about. That’s a wonderful feeling.
The last time that happened was very shortly after I posted my Up to $20 bounty to find Pichu in non-Pichu card artwork thread: @muk found the silhouette of Pichu in the 2010 Team Rocket’s Trickery card:
I guess this is as good of an opportunity as ever to shamelessly plug my blog. I have a blog post called Pokémon Cards Featuring Pichu which documents the 11 different artworks I’m currently aware of which include a Pichu (with pretty pictures) and even includes a couple of close misses where Pichu should have appeared but ended up being omitted. The bounty still applies as well if anyone wants to do some Pichu spotting.