The Disease spell infects the target with an illness, and can only be cast on your territory. They become surrounded by flies and take periodic damage. The nasty ability of this spell is that the disease spreads among the enemy's creatures, and will keep re-infecting them as long as they come into contact with an infected creature. The length of time the creature is infected depends on the strength of the spell cast.
The spell is very expensive, starting at 7000 gold, meaning you should use it wisely. Infecting just one creature will have barely any effect, and they will soon recover. However, if you time it so that you infect one creature with a particularly strong spell while he is surrounded by his allies, they will all become sick as well. This can be devastating to an opponent in the middle of a battle, causing all of their creatures to lose heath and therefore weaken. If their creatures are sent home while still infected, they will likely infect their bunkmates and anyone who passes them, and will be constantly reinfected. This has the benefit of weakening or even killing creatures who cannot Heal, as they will stop their jobs to sleep to recover.
The spell is not as effective against those who can heal, as they can recover the health lost due to sickness. This doesn't mean they can't still spread the plague, so they make effective carriers.
It's also interesting to note the Avatar is almost completely immune to disease, and it will take multiple castings to have any effect at all on him. Not that you should waste time with such tactics, as killing him with anything except brute force is almost pointlessly difficult.
| ||Armageddon / Call to Arms / Cave-In / Chicken / Conceal Monster / Create Imp / Destroy Walls / Disease / Heal / Hold Audience / Lightning Strike / Must Obey / Possess Creature / Protect Monster / Sight of Evil / Speed Monster|
| ||Call to Arms / Chicken / Create Gold / Create Imp / Heal / Inferno / Possession / Sight of Evil / Summon Horny / Thunderbolt / Tremor / Turncoat|
| ||Assembly / Create Imp / Deception / Detection / Electric Shock / Enchant / Exorcism / Heal / Possession / Seismology|
| ||Time Bomb|