Arena is the best mode, change my mind.

Items that are also dank kush.

Situational things on a per-game basis. Are you dying? Buy a Pridwen; at least it also gives you delicious cooldown reduction. Never getting touched? Get a Nocronomicon. Does the enemy keep falling for the "use your ult and send them into your spawn" gag? Get The World Stone. And so on. The more INT and cooldown reduction you have (and the more mana you have, if you have the Book of Thoth), the more you can spam your 2nd ability for high damage. This is your bread and butter, assuming you have the aspect enabled; simply pop your 2 as soon as it's available, try not to die (the sigil goes away if you do), and deal tons of damage for zero skill on your part. Reminder metas are lame and for the squares that aren't tolerant to accept anything other than the meta. This is Arena, and a HiRez game at that. Do what you want.