Oisin's Oath is effectively unusable

Oisin's Oath is a support that makes manna leech come from elemental damage rather than physical. On paper it looks quite attractive, but the intersection of two things makes it effectively unusable:

* It has the Spell tag, meaning it can only be applied to spells
* The vast majority (and maybe all) sources of actual mana leech are either "mana leech from attacks" or are on non-caster weapons.

So there's no way to actually get mana leech on a spell in the first place. This makes the support useless.