DH is a lot of fun if you try to go for as much Ap as possible and get that E to go off and be a flashy oneshot, While I find HOB a lot more versatile and is good going into a lot of matchups.

I believe that Ratirl was running it to see if it is viable into certain matchups ( go look at his op.gg accounts and see the matchups where he takes DH ) (( Links Below to two ))

https://euw.op.gg/summoner/userName=torpedotim64
https://euw.op.gg/summoner/userName=1v9%20machine%20

I run DH when I play twitch support or mid and the enemy either has a way too much poke or way too much engagement to the point where u can not safely stay in lane. Hopefully, you have an ADC that has a mind and can hopefully know how to play safe / under the tower.

while U run around and play support twitch just as u would play river twitch. As river twitch, You are able to steal certain enemy camps ( chickens and gromp, blue/red ) and take scuttle + soak lane XP. ( a lot of fun if u get good at it )

I often find that a level 1 gank top where u hide in the alcove ( make sure u are running ignite) and then force a flash or a kill on the enemy top, because who expects a level 1 gank in top from the twitch support and 99% of the time the enemy is out of position and u can easily get behind them with q ( it helps if you're top has a cc )

Dark harvest scales a lot better with ap and is only viable if u play with a river twitch playstyle ( aka second jungle ) or a very aggressive playstyle of your choosing as long as u are able to keep getting Dark Harvest stacks. U shouldn't be afraid to take some damage for a DH stack as it will eventually be more worth for u.

It is especially good if the enemy has no means of easy escape like a dash, blink .....etc where u can easily get a good W off on a gank or in your lane.

U can still itemize the same by making sure u rush your nashors into Death Cap, and u want to make sure that if u are running DH u get berserker's greaves so u are still able to get all your stacks off ( I personally never go magic pen boots as I find it pointless)

Remember to never build liandrys or Demonic unless u are inting or maybe Aram but that's it
That's about it for what I have to say about that but If u wanna try something new and fun read below.

OK listen here

Its gonna sound strange but trust me its a lot of fun if u are messing around with a duo

................................Moonstone renewed twitch..........................................
Yes yes, and yes, It might sound weird but Moonstone is one of the few items that proc off of twitch passive. This means that u can get free healing off even if u only manage to hit you're W, which is pretty easy to hit. if u pair it with Ardent censer, Staff of flowing water and even redemption + a Death cap and Moby boots U can get insane levels of heals

I recommend this if u are bored of AP twitch and AD twitch and u want to try a whole new playstyle of the rat. ( u can even sub in a Nashors into the build to make it a hybrid AP/SUPP)
I recommend running HOB ( regular AP twitch support runes ) but Guardian is also viable and maybe even Glacial Augment if u are feeling frisky