The wording of the spell mentions champions, which could technically count as a bug. However, all other spells that say they affect champions also affect avatars. Nature's Wrath's DEF reduction is the closest example. If Murkwater Weakness (despite its power) gets treated as a bug, all the other spells like that will also have to be updated unless you change the Murkwater Weakness' text to make it not affect transfigured avatars.
Than problem is avatar explanation right? Maybe there can be something like that "Avatar attack and def can not be changed". It is more like an avatar. Why u ask because avatar can not be attacked other than basic but it s attack easily can interrupted, no sesnse at all.
Some alternate attack abilities that target an enemy directy, like freezing strike, can be used on avatars in any form. There's a fair bit of inconsistency with them and I'm in the process of finding them all to post a huge list in order to eliminate the consistency.
Thanks. It is currently working as intended that Avatars count as champions, but your opinion is noted