Well hello everybody and welcome to my first major suggestion.
I always thought it's odd that there are two bosses in tier 2 but only one in tier 1 and tier 3. That's why I worked on a little tier 1 boss myself:

Rockwood

A construct boss of the lumber family. Like other constructs it resists piercing damage while it recieves more damage from elemental damage. Rockwood can also not recieve sleep. Rockwood deals normal damage.

Now that we got all resistances and such covered, let's keep you wondering about the boss himself a bit more while we explain the floors before the boss.

the boss floors

The floors are called "the Aurora Springs"
The floors before the boss are very similar to the aurora isles. However, parts of the floors are manufactured by gremlins and similar to deconstruction zones. There are also some small ponds (which cannot be reached like the pond in front of the haven bazaar), and some places where there's water running over the pathways (not deeper than an inch).

The backstory of the aurora springs is that most if not all fresh water originates from these springs. Amongst this is the water in haven (yes, the clockworks are moving and pumping water from there to haven is probably hard as hell but just stick with me here). However, measurements have detected that the water isn't as pure as it used to be. Blueprints have been found for a giant lumber so your squad is sent to investigate.

After defeating the boss it turns out the the boss was contaminating the groundwater.

enemies

In the aurora springs are the same enemies as the aurora isles. However, there are also enemies called "Twigs". These are thin versions of lumbers. Their only attack is a swipe attack similar to the ones the retrodes do (they don't have a beam). Twigs also move at the speed of retrodes (they're basically gimped retrodes altogether).

Now for some art (sorry if it's unclear, I did my best at preventing that):

http://i.imgur.com/vLcwalF.jpg

The creature on the top left is a twig. In appearance it is similar to lumber, except that it's much thinner both in body and in arm. It also only has one eye.

Rockwood himself

Now to Rockwood himself. The name is a combination of Rockwell, an esteemed last name, and wood. You have probably seen him in the image. He is a giant lumber, with two incredibly long arms and no legs. The guy is stationary. The gear on the bottom and on his back are continuously turning.

Now for the stage. I used paint because I could use the colours and I'm not a star in other drawing programs:

http://i.imgur.com/cIPRZOB.png

Black lines are impassable walls (or ledges, or whatever). Grey lines are doors. The squares with hearts in them are those healer tiles. The big circle with a red circle in it is the party button. The big orange circle on the top is Rockwood. The blue lines going outward from lockwood are electrical wires, walking over them will electrocute you. The green spawn tiles are spawn tiles and the purple spike bushes are spike bushes, which damage you when walking over them.

Once all players stand on top of the party button lockwood will activate. He consists of two stages:

Stage 1

Rockwood uses two attacks. In addition, twigs keep spawning from the spawn tiles.
The first attack is a smash, similar to lumber. He lifts one of his arms up and smashes it either towards a knight or somewhere between the knights. This attack inflicts stun on hit. His arms work independently and reach throughout the entire map. All parts of his arm deal damage, not just the tip.

The second attack is opening his mouth, as seen in the picture, and firing multiple bullets, similar to the Roarmulus twins' bullet attack. The bullets however do not inflict any status effect and are only shot with five at a time.

During the first stage his body is rather dark and you cannot damage him by hitting his body. However, if during his smash attack his arm hits a spike bush his arm will get STUCK. Once stuck you can damage his arm until he pulls it back again.

When enough damage is done to an arm it will be destroyed and can no longer attack. With each arm destroyed one of the twig spawners will turn into a lumber spawner.

Stage 2

When both of his arms are destroyed you will continue to stage 2. His body will become lighter and now you can damage him from the front. Since both arms are destroyed both twig spawners will now be lumber spawners. He still fires bullets now and then.

Once enough damage is done to the body he will collapse and dissapear. The door behind him will open and the electrical wires will turn off.

the Reward

Players who beat the boss will recieve a recon module : aurora springs and a "Rocky Fruit", which is the boss token for Rockwood and gives you access to a couple of weapons, some pieces of armour and a material. The material will craft a lumber-like tree for your guild hall.