It roots, freezes and damages your targets instantly. Targets will stay rooted for 7 seconds, allowing plenty of time for another strike or a tactical retreat. The three Amplify II glyphs (from Too Many Glyphs) can be replaced with two regular Amplify glyphs from base Ars Nouveau. The current spell in its current state does 25 damage and is enough for most regular mobs, unless your mobs come enchanted/enhanced or otherwise. If you only have access to the regular Amplify glyphs, then this spell does about 15 damage. I tested this using a target dummy mod called MmmMmmMmmMmm. The Accelerate glyph is just there to make the projectile faster and the Item Pickup glyph is well, a ranged loot grabber lol
Disclaimer: At the time of writing this post, I have not fought the wither, wilden chimera or the ender dragon so I do not know how well this spell works against them but I think it's safe assume Snare does not work on the wither or ender dragon. Snare doesn't work on phantoms either.
Update: I forgot add that this spell's power is being increased by a Spell Power thread in a lvl 2 slot on my gear. Without my gear, it does 21 damage. It also uses up about 1/3 of your mana bar without any mana boost enchantments. Mana Boost III on all four gear pieces makes it so you only use about 1/5 of your mana bar.