Note: This is a work in progress guide based off of my experience, and is still a work in progress. There will be more characters and tips as time goes on. Many of this may be very low level advice, but it is to help those in need of match up experience and some Marth help. Advice and Match ups are in alphabetical order.

Captain Falcon

Up throws are good against falcon

Playing aggressively is a smarter choice (Falcon will easily punish defensive options)

Capitalize on platforms (Don't wait it out and expect Falcon to approach as they are not stupid and can easily punish Marth)

Falco

Lasers- good way to work around lasers is to power shield (hard press L or R within the first 4 frames) or try to get into the nice space against Falco

 Fair is a good against Falco as it would space and combo

General

Mix up ledge options - Wavedash off of ledge into grab or attack, come back by attacking, come back by rolling, come back by ledge attack, etc

Mix up techs - Don't always tech towards the stage or away. Always mix it up like tech away then in then get up attack so on and so forth

Stage control and zone 

Double fair - use it at low percentages, to grab, or to punish bad DI at mid percentages

Bad habit #1- Do not always jump right after getting thrown as players will catch on to that habit and punish with a zero to death combo or a percentage heavy combo

Down tilt is a good tool for poking and approaching, but it works better on some characters than others

Do not N-air often as there are better options like F-air. Should be used to defend.

Jigglypuff

Don't down-tilt too much against puff

There are some grab combos against puff like down throw into F-smash at 60-70 percent (note this is with no DI)

Do not grab too much against puff as she can crouch then rest

Do not N-air against puff too much as she can also crouch then rest

Do not up tilt her too much when she is on a platform as she can shield drop into rest or can crouch rest

wall puff by actually hitting her to become a threat. sometimes marth has to get closer than usual to be a threat

down throw to pivot F-smash is a good kill move

Down tilt crouch

Lots of double fairs

Marth - a very different style

Marth is very dangerous against himself as each one has the same range and punishes. Some punishes work best on Marth and very poorly on other characters.

N-air can be used against Marth's d-tilt 

Double fair is a great tool for combos

Up-throw into combos such as immediately going for an up-tilt (if they don't jump) or going for up-air (if they do jump). Note that this works best at low percentages

Marth has a chain-grab against himself by using F-throw at low percentages (this can be escaped by DI-ing outwards)

Peach

Do not down-tilt much against peach

Use F-airs to space against peach

Learn how to smash DI in shield against Peach

Samus

Use F-air in the neutral game and against missiles. It is also a good way to zone against Samus

Do not edge guard off stage against Samus as she can punish you hard.

Keep Samus in the Air as she is weak in the air and very punishable (make sure you are on the stage)

Sheik

Stay grounded against Sheik

Make Sheik come back to the stage by grabbing the ledge when she up b's. This will lead into punishes like wavedash on to stage then f-smash

Up-throw is a good tool which can lead into Up-tilts or Up-airs depending on if they jump or not.