I wasn't commenting on the item, just on your post. =p

is the passive so much of an issue because it seems much more useful than hiding out until your mana regen kicks in and by the time the item is complete it will be at least mid game so your farming would have already been messed with long before the item is complete.
Please continue to support or comment on these ideas thank you. ^^

Yes the mana return passive is a problem. That particular type of mechanic cannot be balanced outside of individual champion kits and it should never be available on an item. Champions are balanced in part on the idea that they will run out of mana without spending a lot to itemize more of it, and mana-return based on using abilities or auto-attacking is far too binary to ever be properly priced or balanced.

i will not discredit your claim but it is only a difference of opinion and also if you don't try why give up, because you have no way of knowing if something can be balanced or priced correctly.
For those who think that item would "break" the game to rush this with nothing else does tend to leave you open for a lot of problems if it ever happened. also its no like there are champions who don't use mana as a resource right? sorry if you find my sarcasm rude. but there are always problems it seems.

For reference, something like mana-sustain was attempted.....The very opposite effect mana burn.

It was always binary because many champions could not afford the mana cost, and some other champions would die before they ran out of mana.

Attack-based and ability-based mana adjustments are very binary because of the large discrepencies in mana costs and optimal builds. It cannot be balanced and worth using for more than a tiny minority of the champion base at any given time, and it is not worth the effort to change every champion so that they can be balanced with such mechanics.

If a mechanic cannot be balanced and worth using for more than a very small selection of any category of champions or it requires excessively altering other mechanics to make it work, the mechanic in question should not exist on an item. That doesn't mean that you cannot balance it within a single champion kit, as there are a lot of mechanics that are balanced within champion kits and would be broken if they were available on items.

honestly there are many items like that already and also with less than 100 champions so far it doesn't really matter if it is for a minority or not and viewing it from a worldly aspect there is nothing wrong with helping the minority at least not from my point of view, because the way i see it many things done to balance or strengthen or weaken champions and items is more so done for the minority or the league, prime example high ranking teams or individuals because most summoners play normal games. Again Continue to comment but please comment on more than one item i have many ideas.

the parasite item seems to strong imo 25% cd increase could crush certain champs.
i like the rest though (the mana regen one is to strong i still like it though).

I have added more items so look at those as well ^^

Lord's Divining Path: Reduce the base Mana gain per hit to 4 and the bonus for striking champions to 4x. (it's a huge change, i know, but if you look at what it is right now i think u can agree it's a bit strong atm)

Looming Parasite: Should not be able to reduce cooldowns below 0% cd reduction (no extended cooldowns, only less cooldown reduction for the attacker)

BBS: Armor penetration should be increased slightly, as this is a legendary tier item and 15 armor pen won't do much (even with the ability to stack it with other armor reductions). I'd say 20-25.

The rest of them look balanced and like amazing items.

But still affects them, which is why Stark's Ferver worked.