In reading the two disease entries that are included in this preview, perhaps our judgement on the spell Contagion is too harsh. The complaints about that spell is whether one of the diseases one can use would easily bypass a Legendary Creature's auto-save feature. The argument assumes that as soon as the victim is targeted by the spell, they immediately suffer its effects. However, in the disease examples in the preview, the symptoms don't typically manifest for quite some time. If that is the case for slimy doom, then maybe it isn't a very good combat spell after all.