I don’t know about this…
Very likely, this will be seen on purple def. With Bane of Mercy cursing all and The Spider Throne webbing on purple, it doesn’t seem ideal… Not only that, Elemental Snap Freeze with Curse All means unless you cleanse it turn one, you’re going to be frozen for a significant amount of time.
So… you’re pushed into using Inari to stop Bane of Mercy from going off, but you’re not guaranteed to have that green->blue 3 match conversion. Despite that, The Spider Throne is immune to mana drain, so that’s going off.
I guess you can use Spirit Fox to zap Bane of Mercy or zap a non-Spider Throne and blank the Bane, but that just gives TST more of a chance to align.
Voice of Orpheus becomes a harmful option, because Curse all + alignment into Elemental 3rd trait hitting VoO means you now can’t cleanse and you’re frozen on Red which is bad for Zuul lovers.
So what is our benefits?
On yellow day, it is basically a Lamashtu. The curse all is pretty negligible as Mercy can cleanse the curse off and Moon Rabbit can neutralize the curse (one of the few times where cleanse =/= bless) to the first slot.
On blue day, it blocks Drowned Sailor’s Yellow to Blue. There’s still limited counter-play for Red to Blue and Green to Blue. I guess it opens up the option of 2 Purple Converters on Blue Day. Blue only counters Yellow, Purple, Brown currently. Bane is just another option at that point. Astral Spirit is not a true counter and the AI can still go off despite gem removal.
(Mercy, Malcandessa = counter yellow, Bane, Moonsinger = counter purple, Tai-Pan/Eldritch Minion = counter brown).
At best, the Curse All can help with your Entangle + Curse All turn 1 or gamble the Snap Freeze on a Blue enemy + Curse All and hope your Elementalist lands a freeze/stun afterwards.
The Bane of Mercy is definitely the bane of Mercy… on your team. Mercy on the enemy team, its not much of a bane shrug.
On non-Guild Wars, you can first slot High King Irongut and use Bane of Mercy to give it attack while making gems/filling Thrall, I guess? All will be eaten…