Thunder's an odd move in brawl. I thought I'd detail its mechanics here.
THUNDER... DRILL.... BREEEEAAAAKAAAAA (Thunder THROUGH platforms!)
•Depending on the distance between the thundercloud and a solid platform, Thunder may go through it and still hit pikachu. Most notable is in Hyrule Temple, where if you're on the lowest platform, you can Thunder and it would go through. Judging by a custom stage I made, the total vertical range for thunder is 8 blocks high. The "cut off" point for thunder begins at the very top of the 4th block from the bottom. However, if there are two consecutive blocks at that cutoff, thunder continues downward through both. To be specific:
POWER OF THOOORRRR! (Invincibility frames)
•Thunder's Invincibility frames are right after Pikachu gets hit by the bolt, but last a rediculously short time.
•They're just enough to detonate some explosives (Bob-ombs, Blast Boxes, Gooey Bombs) without getting hurt. Nova Boms screw you over with their multiple hits, though.
•The invincibility frames also allow you to dodge Marth and Ike's counter, and Lucario's Double Team. Peach's Toad, being the only multi-hit counter, can still hit Pikachu, however.
Two-direction reflection
•When reflected, the thunder goes BOTH ways. (ex: Pikachu jumps over a fox, doing thunder. Fox reflects. Another player knocks Pikachu back in the direction he came, knocking Pikachu into his reflected thunder above fox.)
"It's a Nimbus Cloud. Cumulonimbus is stronger." (Cloud got nerfed)
•The Thundercloud got nerfed in brawl. It no longer does 39-ish damage with multiple hits. Only a mere 10% and they're out of it.
"Hey, Pikachu shouldn't know Electrolevitate!" (Momentum negation)
•Thunder is Pikachu's only attack that negates his momentum without leaving him in a "O NOEZ, I CAN'T UP+B ANYMORE D:" state.
•Using this, Pikachu can stop upward momentum when he falls on a spring, or hover in mid-air on strong enough air currents/low gravity
WE HAET THUNDER (Characters that can screw pikachu over with his own thunder)
•Thunder is absorbed by: Lucas and Ness (Down+B, Warning: heals 30% damage!), G&W's Down B
•Reflected by: Fox, Wolf, and Falco (Down+B), Pit (Side AND Down+B, but down B's a bit harder to land if Pit's not moving foward through the thunder), Lucas and Ness (F-Smashes), Mario (Side B), Zelda (Neutral B), anything wearing a Franklin Badge, and MAYBE ROB (Side B is said to reflect stuff, but I don't see it doing so)
"Oh, it DOES strike the same place twice" (Thunder's multiple bolts in one)
•If you use thunder on one of the Spin Blocks in Super Mario World, you'll see that it seems to get negated at first, but a lone bolt makes it through.
I'll post more as I find them.
P.S.: All these excessive details, but nothing on how much damage it does, lol...
THUNDER... DRILL.... BREEEEAAAAKAAAAA (Thunder THROUGH platforms!)
•Depending on the distance between the thundercloud and a solid platform, Thunder may go through it and still hit pikachu. Most notable is in Hyrule Temple, where if you're on the lowest platform, you can Thunder and it would go through. Judging by a custom stage I made, the total vertical range for thunder is 8 blocks high. The "cut off" point for thunder begins at the very top of the 4th block from the bottom. However, if there are two consecutive blocks at that cutoff, thunder continues downward through both. To be specific:
POWER OF THOOORRRR! (Invincibility frames)
•Thunder's Invincibility frames are right after Pikachu gets hit by the bolt, but last a rediculously short time.
•They're just enough to detonate some explosives (Bob-ombs, Blast Boxes, Gooey Bombs) without getting hurt. Nova Boms screw you over with their multiple hits, though.
•The invincibility frames also allow you to dodge Marth and Ike's counter, and Lucario's Double Team. Peach's Toad, being the only multi-hit counter, can still hit Pikachu, however.
Two-direction reflection
•When reflected, the thunder goes BOTH ways. (ex: Pikachu jumps over a fox, doing thunder. Fox reflects. Another player knocks Pikachu back in the direction he came, knocking Pikachu into his reflected thunder above fox.)
"It's a Nimbus Cloud. Cumulonimbus is stronger." (Cloud got nerfed)
•The Thundercloud got nerfed in brawl. It no longer does 39-ish damage with multiple hits. Only a mere 10% and they're out of it.
"Hey, Pikachu shouldn't know Electrolevitate!" (Momentum negation)
•Thunder is Pikachu's only attack that negates his momentum without leaving him in a "O NOEZ, I CAN'T UP+B ANYMORE D:" state.
•Using this, Pikachu can stop upward momentum when he falls on a spring, or hover in mid-air on strong enough air currents/low gravity
WE HAET THUNDER (Characters that can screw pikachu over with his own thunder)
•Thunder is absorbed by: Lucas and Ness (Down+B, Warning: heals 30% damage!), G&W's Down B
•Reflected by: Fox, Wolf, and Falco (Down+B), Pit (Side AND Down+B, but down B's a bit harder to land if Pit's not moving foward through the thunder), Lucas and Ness (F-Smashes), Mario (Side B), Zelda (Neutral B), anything wearing a Franklin Badge, and MAYBE ROB (Side B is said to reflect stuff, but I don't see it doing so)
"Oh, it DOES strike the same place twice" (Thunder's multiple bolts in one)
•If you use thunder on one of the Spin Blocks in Super Mario World, you'll see that it seems to get negated at first, but a lone bolt makes it through.
I'll post more as I find them.
P.S.: All these excessive details, but nothing on how much damage it does, lol...