The most valuable Pikachu cards typically include 1st Edition holographic cards from early sets, Gold Star variants, Alt Art cards from modern sets, and promotional cards with limited distribution
As for Sai, Master Thopterist, its main value is doubling up our artifacts by making a 1/1 Thopter whenever we cast another artifact, which in turn doubles up the power of our Karnstructs or whatever happens to be wearing All That Glitters
Note that to actually use the interruptions enabled by this combo you must have a monster in your face-up ED and cards with Spell Counters to return to the hand, so you have to decide from situation to situation whether you benefit from this combo
Umbreon Gold Star Japanese PLAY Promotional [BGS 9.5] Publication Date: 2005-2007 Grading: BGS 9.5 Market Price: ~$70,000 (2021) There are a lot of valuable Eeveelution cards out there
You run the risk of having your big enchantment blown up without impacting the board, but who runs enchantment removal in Commander
Unlike "Mystic" used by Blair/Rei, we actually got to see a lot from this anime archetype