[x]keep stat points for later.
first, observe opponent since a mob npc won't have the gamer abilities. Likewise, he won't regenerate chakra like we do, so quick hit and run attacks benefit us more than him. If he is literally a shadow, and that isn't just a cosmetic effect (observe should let us know) then he might have special attacks like shadow teleporting or those tentacles from earlier. Maybe flashbangs or fire might be effective if he's a literal shadow.
We should also observe the seal on the ground. Make sure that it isn't still active and capable of summoning more things during the fight, or that we can't win easily by breaking the seal.
[X] Observe opponent.
-[X] Observe the summoning seal.
-[X] Stay at a distance and be evasive, use kawarimi. Use ranged attacks and if necessary improvised projectiles.
-[X] If he manages to close with us, or when his hp drops low enough that we're certain of victory in a close up fight, try to disarm him.