NS mode causes all sword attacks to have a fire element and cause extra damage. Certain attacks also have a sort of flame shockwave that deal low damage but cause opponents to flinch. I recall fair, fsmash, and dsmash creating the shockwave. I don't remember usmash having it, but it might.
Also worth noting: Ike's uthrow gains the fire element and becomes more powerful.
Quick Draw (Ike's sideB) gains greatly improved knockback scaling, making it a better kill move if one chooses not to cancel it into another attack.
NS mode also adds a few new moves. The Flourish can be done if you hold B while countering someone. It doesn't connect reliably though.
Aetherial Eruption can be performed by holding B during the entirety of Aether. It isn't as powerful as a regular fully-charged Eruption, but it can still be used as a finisher during certain situations.
Finally, Ike can perform a super move known as Razing Eruption. Holding B during side taunt will perform this powerful attack. also no sympathy mode just looks cool