Despite a lack of competitive play and the card being eclipsed in power, the promo version has managed to hold pretty consistent value
Whenever Pikachu comes across something new, it blasts it with a jolt of electricity
So for example, green could have some variation on Autumn's Veil: Spells you control cant be countered by purple spells this turn, and creatures you control cant be the targets of purple spells this turn. At one point, a purple card was designed like this, according to WotC: 1P Instant Choose one: Counter target green spell, or destroy target green permanent, or destroy target Forest. Purple would hypothetically add four 2-color combinations (WP, UP, BP, RP, GP), though green+purple would be rare since those two colors would be hard enemies
Making all your creatures more deadly to block is great value from a 3-mana planeswalker
Life totals going from 40 to 25 and the number of players from 4 to 2 affects how aggro functions in Brawl
We've already been over why the card is good and that's no different for this version