http://puzzledragonx.com/en/mission.asp?m=409 You're going to want to keep this site handy; it's got everything you would ever want to know.
Poring Tower is basically a reoccurring collab event dungeon that has all of the Ragnarok Poring type enemies in it (aside from Archangeling and Deviling, those show up elsewhere). All of the poring type enemies in here come automatically at max level (1) and at your point of the game, they may even come in handy for you in your team for a while. On Master level, you'll fight Demons, which are complete ASSHOLES if you don't have the ability to break their defenses. On Expert and Intermediate, Big Slimes will drop.
What is special about this dungeon is that these poring enemies don't need to be leveled up or evolved to be skill-up fodder (which is a very good thing) and they provide five kinds of skill-up that you won't find outside of event dungeons or REM pulls:
Poring: Armor Break: Skills up Machine and Dark Golem
Poporing: Attack Stance - Wood: Skills up Highlander
Drops: Attack Stance - Light: Skills up Valkyrie
Marin: Attack Stance - Water: Skills up Siegfried and Blue Valk.
Ghostring: Poison Mist: Skills up Lilith.
What this means for you, however, is that you are going to want to collect Marins, the blue blobs. Not only will they be good exp fodder for your Blue Valkyrie, but they also have the ability to level up her skill (which means that the higher the level her skill is, the fewer turns it takes to charge). Valkyries in general are what are known as Heartbreakers (along with Gigas, Siegfried, Cu Chulainn, and Vampire): they take heart orbs and turn them into some other color. Very useful if you're running a monocolor team. What is special about them is that at max level, they can use this skill every 5 turns (which is extremely valuable).
Also, fusing a Poring, Marin, Drops, Ghostring, and Poporing onto another Poring will evolve it into a Mastering, which has one of the best HP multipliers in the game. Fuse five Masterings onto a Mastering to make a King Mastering, which is even better because it comes with an attack boost. However, this requires a TON of Porings to drop and... they don't drop very often, even on Master.
So I suggest running Int or Expert (trust me, save your sanity and avoid Master right now, you probably won't be able to handle it) and collecting Marins and fusing them onto your Valkyrie. Keep one of every other poring type too, because they may be useful for you early on in the game.
Also, less importantly, the Big Slimes are on those levels. This doesn't mean much because they're easily farmable from the lowest dungeons of the game, but they come pre-evolved, which is also nice. They skill up some nice things too but I don't think you have any of them at the moment. You're going to want a Mermaid/Siren at some point because she'll be a perfect sub for your Valkyrie though, (she changes fire orbs into hearts, which can then be turned into water by Valk), and she's skilled up by Big Bubblies and Marine Goblins and such. Just a heads-up for later.
