what if shen had mana instead?

and has an actual proper interaction between his skills? (think Singed's glue + Fling = immobilize)

with him having mana, he can have a lower CD on his Taunt per level (one that's stronger than his current)

and his ult shield would scale off his maximum mana

as for the interaction part, it would heavly relient on his Q.

for example, if Shen AA a Marked enemy with Vorpal blade, using his Ki Strike, he gains a Magic Damage on-hit effect for a small duration.

if shen AA'ed an enemy marked with Vorpal blade, with his shield, his shield gains 50% Stronger.

if shen Taunted a Marked enemy with Vorpal Blade, his Taunt gets 3 seconds Cooldown

also, mana shen would have a better itemization, he would be able to build, Rod of Ages, iceborn Gauntlet, Frozen heart, Righteous Glory, Tear (and with his Qs he'll be able to stack it)