Sea Salt

This guide was copied directly from my guide for all arenas. Here are some tips that helped me beat them all:

The Hunter does not count! I tried him on a couple different arenas and it never counted. He does not have a place for a medal underneath the arena menu (showing which Apostle you beat it with), so I'm assuming this is intended.

Silaris (the mermaid) was by far the best Apostle for me. The fewer people you have the more damage they do, so I use only a few high damage units. My winning combo is one Hermit, and 3-4 Creatures (at the start buy The Creature and then get your Fishmen killed, then buy The Hermit at the start of Wave 2). Just make sure your Creatures are within the Hermit's shield range. Thrown torches (orange circle with X thrown by the guys with red bandannas) go through the shield though, so be careful of those (flamethrower fire is blocked, but curiously not when they use it to fly). If you're having trouble with fire enemies you can try adding a Drowned to the mix (thanks Sassy Stan). She will completely wipe out any fire attack within range, which happens to be the exact same range as The Hermit's shield, at the cost of reducing how much damage your Creatures do (if you're using Silaris).

Swordsman (and to a lesser extent dogs) can easily take out large portions of your group. Dodging them is pretty easy once you get the hang of it. When they get close they'll ready an attack (noted by the 'shwing' sound) and then they'll move in a straight line towards a unit. This line is determined when you hear the 'shwing' so all you have to do is draw a line between the swordsman and your group, and then move perpendicular to that line (ex: if the swordsman is directly to the right of your group, wait for the 'shwing' and then move up so he slides right under your units). Dogs are less deadly and are very weak. Just let them get fairly close and then move away from them. They'll pause and then lunge at you, but if you're moving away from them they'll miss pretty much every time, and are easily taken out when they're recovering from their attack.

Balistas can wipe out your entire group in one hit, but The Hermit's shield can stop it in its tracks. If you hear one fire just hold cn_RT and your Hermit will pop up his shield. Even if your other units are outside the shield your Hermit will survive.

Leave all the extra money on the ground so that you can panic buy more units if you get hit hard. If you see that you got hit with fire or something and your team may go down, immediately buy another Creature. I wiped a couple times because I couldn't tell that my whole team was taking damage and by the time I noticed it was too late. The new unit spawns around where your reticle is, so just aim somewhere safe so you don't spawn him in a war zone.

If you're still having trouble (or have other tips) hit me up in the comments and I'll try to elaborate on my specific tactics (I can also make a video of going through a few waves if that would be helpful).

EDIT: A few people are reporting that they lost arena progress when they closed the game. I personally didn't run into this but I also think I technically left the game running the whole time (I have my box set to instant on so it doesn't actually close the game). Something to keep in mind.