I created an alternative upgrade; besides the effects, let's move on to the unimproved version.
People clearly like this unit too much – they suggest giving it vampirism and unholy word spells (these were different people suggesting it), I find it amusing. I had similar urges to give a bunch of abilities to dwarves – I was so enthusiastic about magical golems that I gave them resistance, mana drain from the hero, and from units, a channel from the archmage, and golem abilities like immunity to slow and infinite retaliation...