Return of the mad Wizard

This storyline follows the remnants of an ancient Wizard's failed plans to ascend to godhood after his first attempt, which was nearly a success before the divine cast him down and exiled him from time and space to another plane. Solomir was too intelligent to be undone by this though, and he used his understanding of the dimesions beyond those of his world to free himself, namely the 6th dimension.

6th dimension
The 6th dimension is the understanding that all of reality is in fact an underlying reality beneath an alternate dominant reality, and the reality in which he exists is only for the entertainment of 6th dimensional deities. He surmised that if he can affect this 6th dimension he can insert himself back into his own reality by the intervention of the 6th dimensional gods. He does this by having the DM insert him into the campaign.

Solomir had mastered the first four dimensions, the basic 3 dimensions and time, and was nigh unstoppable before he was exiled. He had theorized about the 6th dimension but saw no way to use it for his immediate gain so he continued his campaign to rule all of reality through ultimate knowledge and understanding. Once cast out of reality, Solomir had plenty of time to come to understand the nature of the 6th dimension, and this grants him a unique and especially dangerous skill - he is able to hear tabletalk and use that information to his advantage to combat the party.

Once the players catch on the DM should clarify that solomir can only hear what they say at the table, and that the DM doesnt decide what Solomir hears and what he doesnt, but the DM knows he doesn't hear everything. The DM can decide what he hears and what he doesnt based on what is the most fun to have happen, but any plans circumventing the DM's plans will be foiled, making the only way to beat Solomir a direct confrontation on his terms, or to quit the campaign, thus defeating Solomir temporarily until the next campaign.

The DM should insert references to Solomir in future games from that point on - forever. Bonus point if he's already been in previous games before this campaign starts, for that extra creepy factor.

Solomir's Library
The library that houses much of Solomir's findings and knowledge lies in a pocket dimension accessible only by a set of brass keys that were given to his apprentices, used by them on in case they were summoned to convene and report findings to Solomir himself in his study cathedral. The party can come across these keys by any means, but its encouraged to have them find a long-dead wizard or apprentice with the key with a set of instructions on where to use it.

Solomir's library should have some enemies in it initially, this could be swarms of vermin, undead or even pillagers, but in all cases, there is a lich that appears and taunts the party, revealing that much of the library is foreve sealed off by magical wards. The lich continues to carry out his plans with no risk of major interruption with his phylactery safe within. The party will find hints at the locations of where the keys can be found to each of the rooms further below the study.

Solomir's Lairs
Solmir had several lairs spread all across terragard, and the party will find hints at many of them, though not all of them need to be located - the DM can decide the number of lairs needed for the party to begin the final confrontation.
 * 1) Frost keep - This lair is carved into the tip of one of the Winterspine mountains, and needs to be accessed by traversing a dangerous mountain path through frost giant territory.  This lab was set as high as he could get it so as not to let his 6th dimension experiments interfere with his other plans, namely the rest of the continent.
 * 2) Sky fortress - This lair exists in a cave on a floating mote of earth in the Skylands, and was actually a temporary staging area for his experiments on the living races.  This mote happens to be the same one as the kingdom of the Valendrin, being one of Solomir's resulting creations.  This lair can be reached a variety of ways, most likely flight or teleportation.
 * 3) Forest Tower - This tower moves around within the Reaching Forest seemingly at random - but like anything in the reaching forest, it can be reached if you know how.  The only way to find it is to find someone who already knows how to get there, which can be any of the denizens of the forest, be they fey, intelligent creature, or a native race.
 * 4) Lake Lab - a lab built deep beneath the surface of Lake Garrison.  So deep that a race of Kuo-toa have an entire empire between the surface and where the lab resides.  Even the kuo-toa native to the lake dont traverse that deep, for they fear the monstrosities and the latent magics of Solomir's most dangerous experiments.
 * 5) Hill Hole - A storage area for solomir's non-essential discoveries, many of which are incredibly useful but never directly uselful to his plans of domination, and were cast aside. This is a cavern system he had carved out of the ground beneath the Lowwind Hills near the border to the Barrow Downs.

Solomir's powers
Solomir is a master of dimensional manipulation, and can affect space, matter and time. He can spend a round concentrating to make changes at will to a certain amount of any of those three dimension. He can create matter, rewind time, or move things around in space with a thought. This is a limited form of plane shaping as if all of time and space of the planes existed in his divine domain.

Solomir can hear everything the players say out of character at the DMs discretion, but needs to make it obvious he can hear those things quickly, so the players can begin to figure it out. Solomir cannot hear the in-character talk unless he is scrying or has spies listening, of which he has many in his employ.