Deaths Dance. why the item isnt nearly as cool as it should be @meddler and whoever designe the item
Let me preface this by showing what the item actually does
source: http://leaguesetify.com/builder/patch/5.22.1/
Deaths Dance- 3400 gold +65 AD +10% CDR unique passive: Dealing physical damage heals for 12% of the damage dealt (33% EFFECTIVENESS FOR MULTI TARGET EFFECTS) unique passive: 20 percent of damage taken is dealt as a bleed effect over 5 seconds instead
ok now here is a cross post of mine from a theory crafting site ROG
DEATHS DANCE THE MOST WORTHLESS ITEM IN THE SHOP. 300 less gold than bt for 8% less lifesteal and 10 less damage in exchange for 10 percent cdr which is very available already for adc's this patch and the 20 percent reduction passive instead of the shield and BT shield is pretty good
list of single target physical damage sources that dont already apply on hit affects. keep in mnid if an ability applies on hit affects hyrda or bt is most likely more beneficial given the stats of the item.
Muramana and trin force users benefit. its not good with botkr compared to BT
-cait R because u need phys damage spellvamp insteaad of LS -eve e because she has so much physical damage to benefit from the regen -mini gnar e -Gragas e -Graves ??????????????? i dont think his aa gives u more than BT would based on the proc description -hecarim e because he wont be topped off when hitting his e and get diminishing returns because of aoe q -J4 passive again opener damage might be passible -jax q -jayce knockback on e -kallista q her e is multi target -kha zix q one of the few champs that works with the item very few -lee sin already has spellvamp and benefits from hydra waaaaay more -lucian R gonna be mediocre on him BT is just as good -MF double tap second hit???? -Naut passive -panth Q not that good on him over other items -quinn passive and e possibly better than a bt -rengar e but prob gets more use out of hydra -reksai e but he wants the true damage part -talon q part 2 not part 1 because part 1 benefits from ls -shaco knife -udyr tiger -urgot the one of 5 users who want this over other items the only one fore SURE that wants it over other items besides possibly kha and yorick -vayne e -vi q -yorick qe and r probably usable
so of the practical users we have like 6 champs olaf (because of the defensive passive) yorick hecarim kha for melee quinn urgot jayce and ezreal for ranged and possibly graves
Back at the beginning of season 3 they tested out lord van dams pillager which had AD and spellvamp AT THE TIME.
The big reason this item never hit Summoners rift i because it benefited olaf and lee sin more than characters like talon and so we got black cleavers and other items. Now again we see champions who we dont want abusing it to be the only plausible users
s5 comes in and we get
the item they are now imitating with deaths dance. Riot now has a huge sample size of the effect that we want. healing off of physical damage without diminishing returns in an aoe
I fully believe riot has the capability to balance Deaths dance to be a damage item available to a larger portion of the cast than i listed above especially given the data they received from 
TLDR: deaths dance doesnt heal as much on aoe spells and there arent very many single target physical damage spells that dont already apply lifesteal when they hit making deaths dance a bad item in regards to both playpattern and cost efficiency except on a few abusive outliers like yorick and olaf.
hecarim already heals in an aoe for all the damage he deals with no diminishing effect

Malzahar would like a word with you.