He's talking about Marth's 360 degrees walling ability in the air.
On top of the safety.

As a Marth player I'm not very good against Warios since there aren't that much online and the only one I've ever fought was Ganondoof. Any tips?

He is a strong player, so it's OK if you lose. I do too.

Marth counters Wario, so if you're losing to Ganondoof, he's straight up outplaying you.

Wario has a tough time dealing with disjointed characters. Wario has like, no range, so Marth's aerials can counter all his approaches. Wario will be looking for you to whiff something, so play patiently and don't mindlessly whiff stuff and it should go smoothly for you.

You probably just need to improve as a player.

Here's a tip: stick with fair for walling, and try to not let Wario get under you. Once you land a hit, turn on the gas and try to take advantage of Wario's poor recovery, e.g., fair -> uair -> grab -> fthrow -> tipper fsmash or something like that.

a friend of mine wants advice against marth, he's a falcon/link player

i play marth and it'd be fun to have more even games, any tips for marth's weaknesses?

He has weaknesses?

Well the best advice i can give you is stay on the ground/low to the ground more than you would against other characters. Besides that you are just gonna have to learn from experience

wow, did the hitbox fix make Marth that great? i remember him being terrible before they fixed his tipper

alright, stick to the ground.

Now marth is still really, really good on the ground, but he has an insane amount of anti-air potential. He isnt going to be easy regardless of your strategy

Marth is Aight,
tell your friend to practice Dashing into shield to bait out grounded attacks, then Nair(ing) or UAir(ing) OoS as falcon.... admittedly for a Ranged swordfighter SSF Marth has pretty quick start up for allot of his moves but close range pressure is still effective. Marth still gets juggled easily so don't be to shy to UAir... Surprise DownB's outside of tipper forward smash range is wavy, but you'd have to adjust to marths range.
downthrow to knee 80% K.O.
^^Down tilt to knee works even better.
Mispaced an aerial..? > Forward tilt !!
The gentlemen combo works well
Don't forget to SHORTHOP...

IDK what to say about the link v marh MU though.

In terms of balance/viability don't think marths tipper adjustment is much of a difference maker... he's just easier to use...well imo

just to add a little detail to this:
- dthrow to knee works, but you have to guess the opponent's DI, as they can either DI in (full hop -> knee) or DI out (run forward -> full hop -> knee).
- dtilt to knee is also affected in the same way, and I often find it more difficult to connect than dthrow -> knee.
- a reliable way to combo into knee is a simple uair -> knee or stomp (dair) -> knee. a lot of other moves such as nair will also combo into knee at some percentages. you don't need to learn these off by heart, but you should be able to react to situations where you think the angle is right to knee them.
- gentleman is alright, but I feel that the first hit of jab works better, as it has many uses:
-- jab -> knee is a true combo at higher percentages (around 80% should work).
-- jab -> grab should work at almost all percentages.
--- these 2 options are almost always better than the full gentleman in my opinion.
- in general, as Falcon you will want to dashdance just outside of Marth's shorthop fair range, and try to bait out an unsafe approach. once you see an opening, punish them for it. repeat until victory.

Marth's main weakness is that his hitboxes are kinda transient: he doesn't have sex kicks or any lingering hitboxes, so his moves have openings. Try to use this to your advantage by baiting out laggy moves and using your speed to run in and get hits.

If you are slower than marth god help you

and his moves dont really have a lot of lag to them, its kinda easier said than done

Agreed. There isn't much lag at all.

There isn't, but enough to make things like double fair punishable on read. He kinda wrecks characters like Wario that can't get in, but unless you are one of those characters it isn't that bad.