What reliable tools does Yoshi have other then egg toss and pivot grabs?
This is the ultimate question and the answer is that Yoshi doesn't even have egg toss to work with him. Personally, I say Marth Yoshi match-up is either 65:35 or 70:30.
A big factor in the match-up with Marth is off the edge fighting. Out of almost all characters, I'd say I am most afraid of the potential that Marth has for gimping and plain killing Yoshi while off the stage.
Here is a breakdown of when Yoshi gets hit off the stage:
While he is far off, Marth can jump off and go straight into repeated fairs. Because Yoshi only has three options, attack (stupid because your attacks either have long startup time or low priority), dodge (stupid since he can just fair again once your invincibility goes away), or DJ air dodge (only viable option since you MIGHT get away), he can get slaughtered so easily.
Also, if Yoshi makes it to the edge, dtilt, fsmash, dair, and side-b easily await you. The safest move Yoshi has from the ledge with most characters is to drop, followed by double jump into some mix up which can include anything from air dodge, attack, ledge grab again, or nothing. In each of these instances, Marth has a strategy to combat all of them with relative ease.
One of the absolute biggest problems with this match-up is Marth's side-b. Yoshi Does Not, under any circumstances, have a way to beat the move. A marth can spam the hell out of them move and beat a Yoshi. Why? Yoshi's shield. Because of Yoshi's extra time OOS punishing, you can't punish Marth's side-b at all, let alone spot dodge it. Because of this and the fact that Marth's side-b is one of his bread and butter moves, Yoshi gets owned. Not only that but if Yoshi does one of his main kill moves, fsmash, and marth shields it, he slides right into tipper range for his fsmash...ridiculous.
So marth outranges and beats yoshi close range. So you say, well how about egg tossing and spamming to beat him? Doesn't work. Because of the way that marth dashes (very low and quite fast), you will get instantly punished for ETS'ing even twice. Yoshi's egg is not made for keeping marth back. Along with that, I'm fairly positive that marth can side-b eggs, so that is a sage approach with no punishment.
The strange thing about Marth is that he cuts off Yoshi's moves so badly that he forces Yoshi to do things that are more dangerous because Marth destroys his "safer" options. Instead of drop off edge->DJ, we are forced to use a ledge jump or get-up attack. Instead of spot dodge or shield an attack, we are forced to either take it or roll. Instead of egging to keep him back, we are forced to play his game the entire time. It is an uphill battle from the get go and does not get easy once you learn the match-up. This is easily one of yoshi's hardest match-ups in my opinion.