Arsenal

Plague Arks
From the Old Testament book of Exodus come the Ark of the Covenant.  The God of the Hebrews instructed the tribes to build a vessel in which the covenant with Israel would be stored.  The ark is two and a half cubits long, a cubit and a half wide, a cubit and a half high, it had four rings, two on each side through which ashen poles were placed in order to carry it.  The lid was crowned with two griffin like angels.  When captured by enemies the presence of the ark caused disease and madness.  The plague ark is a deliberate perversion of the actual ark.  Built the same way, but instead of gold it is coated in a mixture of paint and the blood of those involved with its construction.  The inside is filled with sand which should fill the box half-full and cover the Unraveling Rune burned into the bottom of the inside of the ark.  The ark can be used in two ways.  The first is the more subtle and long-term method.  The ark is constructed and then hidden in or near an energy nexus from where is can cause the most damage.  Possible areas would be in the sewers underneath prominent areas such as downtown areas, town squares, office buildings, churches, theatres, arenas, etc.  The magic of the ark will gradually inflict potent nightmares and madness upon the city and wear the world barriers thin.  The second way to use the ark is much more immediate, but much more risky on the part of the builders.  The lid is removed and the builders carry the ark openly through the streets.  The effects are the same though much more potent, and the barriers are much weaker in the presence of such a powerful weapon.

Plaguebearer
Go into a meditative trance after purifying oneself for whatever amount of time one feels appropriate, keeping in mind that in most cases the longer and more encompassing the cleansing is the more potent the spell.  Once in this meditative trance you will shape the energies of reality into an act of creation and summoning.  You will visualize a virus spirit, once it is the only thing you are focused on feed it energy, make it stronger.  After the spirit is empowered summon it to you, this can be done in whatever manner you choose.  For the sake of this example I will say that one should summon the spirit through inhaling smoke.  Then one breaths the smoke into the host of the virus spirit, be it an animal, insect, or other person, even oneself.  The virus spirit can then propagate itself using the host.  The affects of the virus spirit depend on what sort of spirit you choose to conjure up.  Also, wear a sigil of protection so that the virus cannot affect you.

Poisoning the Spirit

In a ritual vessel mix an amount of wormwood with water.  Focus your will upon the mixture and breathe a visualization of the Unraveling Rune into the vessel.  Once this process has been repeated enough times that the caster is no longer comfortable keeping the vessel in the home, it is ready.  Take this vessel of spiritual poison and deposit its contents into the drinking supply of whatever populated area one is targeting.  Ingestion of the tainted water will over time cause madness, nightmares, and thin the barriers within those affected persons.

Gates
Portals and pathways between the worlds still exist, usually in sacred or strange places like haunted places, remote or isolated wilderness, certain landlocked bodies of water and other places in the waters of the world, etc.  There is nothing that can stop you from opening a gateway and leaving it open, in fact holding it open.  Simply find a place whose energies seem to be conducive to a pathway, and rip a hole in reality and hold it open.  Use portal runes to make the gate, the power focused through the runes will hold it open.  Remember to check back from time to time to keep the runes fresh and in place.

Magical Gifts and Giveaways

This one is fun, and not quite so invasive, much more subtle but effective none the less.  Make little talismans and single spell items, rune jewelry, and other such trinkets.  Give them away to random people.  Sometimes they will refuse, others will take them and leave, and others still will remain with interest and questions.  All of them will be effected on some level.

Art and Music

These mediums are also just as effective at producing, channeling, and expressing magic as they are emotion and thought.  Listen to the tribal music of the ancients and you will know.  Read some folk myth and you will know.