Question: In my story, there is a character that is capable of using magic or an ability that allows them to "teleport" as long as they are in contact with the ground or the area that they want to use it on with at least one hand.

For example, in the middle of a circular arena 100m in diameter, as long as they are touching the floor (with a hand), they can teleport anywhere as long as it is "connected" or still physically part of the arena (which means that any floating rocks won't count, and they wouldn't be able to use it to get away from the arena in the case that it is floating).

What limitations can be set on it to avoid being too powerful, and with limitations in mind (or not), what would be the best type of magic/ability to use with it? (disregarding earth magic/manipulation)

My thoughts were to limit it to 75-100m and only usable every second or two, and to be used with wind magic mainly (if mist or fog can be made using wind magic).

Answer: 
**Make her as powerful as you imagine she is.**

Because that is where the awesome is! You worry your character will be overpowered which means you can imagine her doing overpowered stuff. You worry she will be able to do stuff no-one can counter. And I think you like it. **Have her do that stuff!** Please! Have her totally thrash her opponents with her overpowered skills! That is what I want to read.

But then how to beat her? That will be more fun to figure out than how to limit her. You do not need to figure out how to limit the character you can imagine. You need to imagine other characters on her level. Figure out how her opponents can best her or at least equal her. Or team up with her? Woo! Yeah!
First, you already limited the most unfair application by limiting it to ground use :
The dropping someone off in space and coming back.

This was also only usable if you allow forced teleportation of others. Which you can limit (maximum weight, maximum volume or needing the consent of other living beings to move them)

What you were going for in your thoughts as limitations are frequency and range. And those can be linked to have an adaptive cost:

* Teleportation can take time to prepare and the longer you prepare the farther you can go. For example, by preparing 1 second you can just teleport 1m away but if you prepare 1 minute you can move 100m in one go.
* If you need reflex teleportation, you can reverse the relation to time and instead of preparing you have a cooldown during which it is impossible to teleport after teleporting.

You can also make a limitation on precision. The farther you go, the less precise the teleportation is, which could be dangerous depending on how teleporting in a wall is handled.

As for what magic to use in addition to it, I don't see why that'll be necessary, adding anything in addition to teleportation is already overkill.

You thought of Earth Magic manipulating the ground and changing what's accessible, but that's true for any magic creating/manipulating solids (Ice at least and Plants if you allow teleporting through living beings). Now if you really want to add magic, there are a few kinds that works well with it:

* Any Illusion Magic that makes it seem you didn't move yet
* Any Stealth Magic that allows to teleport undetected
* Any long range Magic that allows Hit&Run tactics

If you want another magic, that seems to combo well but still have limitations, any other contact-based magic will work well.