Demonic Embrace Is Mainly used for the sustain it gives you in team fights rather than the burn. Having this just keeps you alive for a little longer which means you can land 1 or 2 Q's before dying if your caught in a bad situation.

Void Staff Is incredibly useful in terms of tank shredding and damage in general 10/10 item since it gives you more purpose than poking backline or ranging melee champs.

Rabadon's Deathcap Is one of your 5-6 items along with Horizon Focus Since the price is a little hefty for it's actual priority. Zhonya's you can use with your E and it can also increase you're survivability and doesn't offer much other than damage, which is good but Oblivion Orb, Morellonomicon, Demonic Embrace would be more useful

Banshee's Veil is only if they out poke you or hit you with ranged heavy attacks ex. lux ult / Karthus ult

Morellonomicon is anti life steal and is good against champs like Aatrox, Yuumi or any other champ with a lot of base healing. On top of that you should also run this against anyone building life steal. Items like Bloodthirster, Immortal Shieldbow, Oblivion Orb is your cheaper option

Rylai's Crystal Scepter is for people with a lot of escape or very high movement speed. ex. Garen, Sett, Singed.

Horizon Focus is only for out ranging your opponent. better for melee champs since you can W and keep them at a comfortable range while Q'ing them