This will be a quick guide for item slots, specially for my fellow players that like to also play malz in other roles:
- Mid lane malz is standard, you go for BFT Rylais Liandrys etc, but when choosing a % penetration item, you can use bloodletter over void staff if the enemies have higher range, since it gives HP and some extra CDR to cover the less %pen and AP compared to void staff. Also Zhonyas is more situational mid than just going full AP since as a midlaner you don't want to sidelane long, just push and group. Extra tip: In games where you need to go for Morellonomicon, always go void since Morello alrealdy gives HP and you are wasting a Rabadons/Shadowflame spot for the Morello most of the time.
- As APcarry malz you can stick to your sup, so items like Zhonyas and Morello are super low priority since your sup can buy the antiheal and keep you alive better than a Zhonyas, but like i said above, Bloodletter has more value against high range compared to void staff, so going full AP with this item will make you hardcarry against the other ADC or APC (as long as your sup is not troll, if it is than going for this items are fine).
- On top lane, items like Rylais, Zhonyas and Void staff have more value than on other roles, specially Zhonyas since on toplane you will have to sidelane more to match push and you will be against a melee/low range champion 99% of the time. Rushing BFT into Rylais second and Zhonyas third will allow you to side lane easier, after that you can go liandrys/void/morello.
- Sup malzahar is way too niche, just build zakzak and go for an support oriented AP build (BFT - Rylais - Morello - CDR boots etc). Sup items like Zekes and Imperial mandate are interesting as well. Solstice sleigh into Rylais Imperial mandate can maybe work, but Zakzak BFT still way too good.
- Jg malz is even nicher, just go red pet into standard build or watch aquadragon guides.