Counter Tips

Edgeguard with Burst Grenade before he uses Quick Attack. Skull Bash has enough end lag to become predictable once you know how to use grenades. Remember, hold B to time the explosion.

Keep your distance. Air needles very close to the ground into fsmash, fair, dash. Mix it up with safely-timed Burst Grenades to distract, bait and punish, as Pikachu definitely wants to avoid those.

Have something ready for when Pikachu lands onto the platform with Quick Attack. Dash, fair, dtilt, air needles into combo, any smash attack.

Pikachu's speed is difficult to trade with, but some safe options are jab, dtilt, ftilt, and all air attacks except up air, which should only be in a combo. Use smash attacks only to punish or combo.

Thunderjolt gets sucked into Burst Grenade's vacuum (while BG makes the sucking sound), which then pulls straight at Pikachu to explode, if TJ is in the first couple frames (close to Pikachu).