Like most items in League, Zeke's Harbinger is Situational. You should only really build it when you think it's good to be built.
What is Zeke's and why is it good?
+50 Ability Power
+10% Cooldown Reduction
UNIQUE Active - Conduit: Bind to target ally (60 second cooldown).
UNIQUE Passive: When within 1000 units of each other, you and your
ally generate Charges. Attacking or casting spells generates extra
Charges. At 100 Charges, causing damage consumes them, increasing your
and your ally's Ability Power by 20% and Critical Strike Chance by 50%
for 8 seconds.
Firstly, the stats you get from the item are very good stats for many supports. Zeke's gives supports a little bit of armour (which in most builds, support's don't get at all) to protect them from enemy Auto-attacks. It also gives a fair amount of mana and AP, and 10% CDR, which makes it quite viable to replace another item on a support.
Secondly, the passive gives you and your ADC +50% crit chance, and 20%+ AP, but you or your ADC rather should keep an eye on the charges (Don't waste them for farming when a teamfight is about to happen). In the late game, a usual ADC build gives an ADC around 50% crit.
Let's use this as an example:
Hurricane and RFC give 30% crit each, so in total, this build has 60% crit. Meaning most of the time, an autoattack would be a crit. However, 40% of the time, the AA will not crit and only do 100% damage, vs. the 250% damage you can get with an Infinity edge in the build. Having zeke's active means that your ADC can do 250% damage every attack for 8 seconds, which is massive.
Herald works well on Champions that
- Benefit from the stats
- Can stick close to and help their ADC
Zekes can be a good buy on champions like Soraka and Sona. Both of these supports excel at sticking by their ADC, with Sona's movespeed buff, and Soraka's movespeed buff towards damaged allies. Both of these ADCs benefit from all these stats. This allows them to stick by their ADC in a teamfight, and help them buy charges, before allowing them to do 250% damage for 8 seconds, and heavily damage the enemy's front or backline.
Who is Zekes bad on?
Zeke's provides good stats for 'mage like' supports, but is quite lacklustre for Tank supports, it probably shouldn't be built on supports like:
- Tahm Kench