Why do you say, "never" to lich bane on Diana. She can proc it 1 - 3 times depending on how long she wants the engagement to be in a fight. That's literally giving her 1 - 3 extra 75% AP scaling spells that will be stronger as she gets more ap. People always go for this "tanky mage" build, but if you have experience on the champ you start to notice it's not strong enough to compete with the current meta. If you ever rush abyssal scepter, you itemize for your lane opponent, and end up being useful against other lanes, so the item ends up being garbage unless the enemy is full of ap. Zhonias is always mandatory, but it's high build demand ofa needlessly large rod can be hard to farm for diana, especially when not itemizing aggressively or defensively against your lane opponent with a seekers armguard. From alot of testing I find the best way to go is Lich bane - Zhonias hourglass. Lich bane's procs means you'll always outdamage your enemy opponent, assuming you get out 2 probs at least, unless he built the same item. If you rush zhonias, which is still situationally good, building abyssal after it really doesn't work out as much as people would like to believe it does, as straight up rabadons gives you much more damage, and a measly 45 mr, that the typical midlaner matches up with 40 mr from athenes truly doesn't make you as tanky of a mage as people like to think it does. The only way to truly be a tanky enough mage to prevent getting instantly blown up is roa, and that doesn't work properly on diana. So in my opinion, and practice lich bane - zhonias - rabadons - sorc shoes - void staff - ga provides for alot more damage than having abyssal scepter instead of bane, and only trading a measly amount of magic resist that's only prevalent very early in the game and results in you being **** over by other people in the game.