Frost Queen's Claim needs a buff.

Currently, it's a bad choice to upgrade your Spellthief's Edge.

Do you need mana regen? Mikael's/Athene's/Morello all give way stronger mana regen. Do you want AP? Literally any complete AP item other than Ardent Censer will give you more AP. CDR? You're better off with anything else.

The only thing it currently has going for it is the nice AoE slow active, but even then it's not worth it if you're wasting an item slot. You will still run oom, and your damage will still suck.

The way I see it, there are two ways to go about buffing FQC (Frost Queen's Claim). Either buff the mana regen or buff the active.

Before the regen rework, FQC granted +10 mana regen. That was the same as Morellonomicon. After the regen rework, Morellonomicon now grants +100% base mana regen while FQC grants only +50%. Imo, FQC should grant 100% since these two items granted the same amount before. FQC's mana regen was stealth nerfed for no reason.

(Edit) Another way to give FQC it's mana regen back would be to tie a mana restoration to the active or to the Tribute passive. For example, landing the active could restore X% of your maximum mana per enemy champion hit. Alternatively, activating the Tribute passive could restore X% of your maximum mana. Credit to player Vonler in the comments section for this idea. (/Edit)

The other way to buff it is to make the active stronger. If Riot decides to keep the stats weak, then they should at least make the active worth the gold spent. I propose adding an AP ratio on the slows decay (like Lulu's Q before that mechanic was removed). The slow would decay from 80% to 10% of your AP. In other words, having 300 AP would mean the slow decays to 30% instead of decaying to 0%. Another possibility is to add an AP ratio to the damage portion of FQC's active (which is currently a pathetic 50 + 5 per level magic damage).