Rifts
There are four types of rifts.
Basic Rift, also known as a Wizard's Child. They suck up all utilized magic in the world and output it tame (Not really tame. But better than letting it manifest into lightning and ripping holes in reality.) ways. Crops can take longer to grow, fires might start, and water can spawn. Worse things can happen, but that's the basic thing.
Next, you have the Infernal Crack, also known as "WHY!!!"
These will spawn pigmen like no other. It absorbs magic again and outputs in more malign ways. Some theories say this is because the hole is to the Nether, or rather, so close that it cannot escape into the Nether, so it stores it and curses you tenfold. Some theories say the evils of the Nether go into your house, as they hope beyond anything to find a way to the original world.
Lava can spawn, ghast fireballs spawn, lava slimes. Fires spring out, all sorts of ancient spells and evil leak out. (I.E. you could get swiftness in a RARE chance, it's more likely to get withering or something.)
The Endish Void also known as, well, Fear.
Run. Move from this rift, get literally faaaar away from it. You will have like, sixty endermen in your house per day. Also, the End is a brewing pot of Thaum. You will be afflicted with every curse. Slowness, Weakness, both Mark V.
Endish Rifts are always near End Portals. They rarely spawn away from them, but 67% of the time you'll see a Endish rift at a Stronghold/above a Portal.
Infernal Cracks can also appear if you abuse some sort of Nether-ish device.
Remember, these cracks (Except the Basic Rift) spawn when the pathways to this place is weak.
Basic Rifts RARELY can be created, as they're really pocket dimensions with a pathway to your base. Maybe you can create one if you tried.
Basic Rifts have a higher chance of occuring in or around those Village towers (I guess they are churches?) and in Witch Huts. Also all the pyramids!
Imprints
Imagine a deep imprint of utter magic into the earth itself.
These imprints bleed epic-ness. They bleed out Thaum, so you think. In reality, this is an odd, broken form of Essence, converting to Thaum, (Make up why.)
But, you can fix this form of Essence. It is a older, more powerful form of Essence called Imperial. The Imprints will break down into High Essence, then into Low. After that it produces nothing (Maybe a Unit of Thaum per day.)
These are usually found in Witch huts, or Nether Fortresses. (Also on a mob spawner. Who knows what kind of wizardry goes into THOSE.)
My ideas. Butcher them as you will, Green!