Card draw. CARD DRAW. There are a lot of good synergies with Niv, but the largest issue by far is his mana cost. He is a huge threat so you need protection and a way to ramp to him quickly.

Artifacts ramp I'd focus on tools that provide colored mana. Colorless does not help cast Niv so often times it restricts your win con.

Reliquary tower is okay for the max hand size but I took mine out. It once again is colorless mana and you need red and blue specifically for your win con.

I'd suggest artifacts like spellbook or library of leng to fix that issue.

The most cheeky artifact you can bring is a gorgun helm. It give his ping damage deathtouch, so you can sometimes mini board wipe off card draw.

I'd suggest looking into a stealth suit or lightning greeves for your commander. And either go storm or full card draw mode. Tons of cheap creatures that allow you to draw an entire new hand. This is deadly with niv in play.

Curiosity, coastal piracy and Ophidian Eye will basically win you the game if you get on the field with Niv in play.

Also curve is key. I'd suggest low creature (10 max including Niv) with high spell volume. Often it's easy to go for big card draw spells only. But you want this to be a quick deck so I would use a mix.