User blog comment:Willbachbakal/(Summoner Spell Concept) Streamlining Summoner Spells/@comment-24862418-20161017152728/@comment-26378838-20161017202955

" in particular has no cooldown on his empowered abilities, which comes into play immediately post-ult, so unless you're willing to change that, zero resource spending would break him."

Oops, forgot about that. Of course some changes would be needed to avoid breaking the game.

" and also somewhat stretch the definition of "resource": is it really a resource just because it's displayed on a secondary bar? Does something need to be displayed on a secondary bar to be a resource?"

I personally consider a resource any consumable resource that isn't an active function of an ability. For example, I consider the stacks of to be a resource even if it doesn't appear on any secondary bar, because they're consumable and can be generated by any ability, much like  Ferocity. That also excludes things like traps or ult charges. On that vein, I consider both shields to be a resource, since they can be refilled by abilities/movement and aren't tied to an active function of a single ability.

"What does it mean for a shield to not deplete? Would that mean Morde and Yasuo would have pseudo-damage immunity (...)"

I was thinking more on the lines of that odd mechanic had in URF: he couldn't cast is ult again if the mana requirement went beyond his mana pool, even if in that mode mana wasn't used by abilities, so a shield that couldn't be depleted would only do so if the incoming damage was below the shield threshold; in other words, if the damage is higher than the shield amount, the surplus damage will still go through even if the shield is up.

In summary, it would be pseudo-immunity to sustained damage, but burst damage would still go through, even if lessened.

"(...) wouldn't that sort of tread on Barrier/Phase?"

Only on and. Other shields don't hold the same properties these shields have to be considered resources, so I don't think such a spell would tread on your proposal for Phase.