Hexdrinker is indeed an overloaded item (Warning: Math) (TL;DR at Bottom)
is overloaded and ill explain why.
Stats (without the passive):
+20 ad +35 mr
One
comes with 10 ad and costs 350g
Meaning the item comes with 700g of gold so far (20 ad)
One
comes with 25 mr and costs 450g
This means that 35 mr is equal to 630g
- 700+630=1330
Hexdrinker costs 1300 gold, MEANING IT IS ALREADY 102% GOLD EFFICIENT WITHOUT THE PASSIVE.
Now, the average level you will back and buy this item is level 5,6, or 7. Lets say 6
Keep in mind that Hexdrinker is a magic shield, meaning it takes your total mr into account and it is not just a negation of X damage.
- Assuming you have 9 mr from runes (average), and the average midlane champion will have 33 base mr at level 6, you will end up with 42 total mr before Hexdrinker.
After Hexdrinker, you will end up with 77 total mr at level 6.
77 mr calculates to roughly 44% magic damage reduction.
Hexdrinker at level 6 will negate a base of roughly 167 magic damage.
Taking the 44% magic reduction into calculation, Hexdrinker results in a total of roughly (sorry for the overusage of this word) 240 magic damage negated.
150 health for 400g
Meaning 240 health would be 640g
Considering Hexdrinker only blocks magic damage and not physical (not counting true damage because it is very uncommon and only like 2% of the overall damage in the game), the 240 magic shield calculates to be worth 320g.
1330+320=1650/1300=just under 127% gold efficiency.
This is cheap item that is incredibly gold efficient, 127% to be exact.
TL;DR: Hexdrinker is a cheap item that is 127% gold efficient with its passive and is therefore very overloaded.
I am going to take a nap now because my head hurts from all this math.
Here, this item is shit and Hexdrinker removes an AP champion from the game for the half of the match. I know, no math, but fuck Hexdrinker.

reworked to have zhonya's active, why not?
is the duskblade of AP