In general transmuter spell cost is so high in group vs group fights they run out of juice long before the fight is over. They don't work all that well, specially at hero lvl using metabolic spell in pk is just wasting mana. In general vs 3-4 people just to get them slowed down I have to cast it multiple times. Considering they are useful in extremely dangerous situations and how much mana it costs. I would like to see them work a lot more often.