I haven't read what you guys have said about Marth yet, but I can give a little real simplistic information.
1. His neutral B, Shield Breaker has the following qualities: It breaks shields in 1 hit fully charged, and brings them down to the size of a pea with an uncharged. If it hits with the tip, it has the most knockback of all of Marth's moves. If used in the air, it will propel him forward a lot, and can be used for recovery. (I'm pretty sure the hitbox is only out the first few seconds, while he is flying forward, it's no threat)
2. His Side-B, Dancing Blade: If the third hit is angled down, it can be used as a spike. If the upward combo is used, it sets up very well for his aerial combat. The side combo can be used as a mediocre, but fast killer. The down combo can be used as a damage racker. He will use it to turn around, and it has a very fast start up time.
3. Up-B, Dolphin Slash: It has invincibility frames on startup not sure what they are though. It's auto-sweetspots, and it is actually a very good killer.
4. His Dair is a spike, but it has TONS of lag, he will rarely ever use this, and if he does, it will never be on the stage. If he does, and he wiffs it, make sure to punish.
5. His Bair turns him around, that's pretty much it, but it's still powerful.
Also, I know I'm kind of late on this, but I did some research on ZSS's spike. It turns out, if she has perfect spacing, and you're right next to the edge, she can D-Smash > D-Smash > Down-B spike as low as 17% on Lucario, and you will die. It's not much of a threat until around 50% though.