Yeah, Lissandra's passive could be improved somehow, but I feel she does have some very specific strengths, namely early game mana advantages and her lack of targeted spells except her ult which she can also self cast. Why is that helpful?
WHERE DID TEEMO GO?!?!?!?
It is very, VERY satisfying killing a scared teemo when he doesn't want to move. Just W-Q-E-ALT+R(self cast ult) and he's dead... I swear it was so funny seeing him rage at me. But also she has great ability as a peeler for your ADC, and sometimes it feels good seeing an enemy run away from something that popped out of nowhere and just shattered them before...
Excuse the pun
But anyways, the passive could be changed, but I don't have any good suggestions sadly. Mana restore AA proc already exists on Xerath, but I feel the part about reducing the CD on Liss's passive whenever she impairs an enemy's MS is part of her identity as a CC goddess.
But Rito plz, add puns for buying items for her
Frozen Mallet (why buy, idk, but as a joke like the Primetime Draven AP item) - "Another tool for my victory"
Iceborn Gauntlet - "They will fall beneath my fist!"
Frozen Heart - "Oh! A tribute to my personality"
Forst Queen's Claim - "I remember when my mother gave me this as a gift... And now it will bring me to victory!"