This is my Zarus build that I use for a quick jungle and early lane assassin for nitro players.
It consists of:
• Mindrazor for the aoe basic attacks and to start the mana to physical power scaling
•Basilisk for the armor reduction and to hawk them down if they try to run
•Syonic Echo to speed up jungle camp clearing
•Resolution for more mana and mana% added to damag output with mana scaling whilst clearing camps
•Tainted Blade for heal reduction and stronger ability damage
•Then any penetration or armor item of your choice.
Let me know if adjustments should be made