The FDefender Z's drop Level 2 % 3 key spheres at Over Kill & sometimes w/o, I'dv seriously consider fighting down there for easy cash, Rikku's Godhand nets yoy 100,000 Gil when you beat mimics, remember the more u fight the easier it will get.And I back Alexhocker's sentiments, get a weapon with First Strike if you have not got good armour yet as Great Malboro's ALWAYS Ambush u down there, would could have the sphere grid maxed & still get pounded by Status if you have ish armor, I suggest completing the Arena sidequest for 99 Dark Matters & gettying Ribbon or even getting Stoneproof, Confuseproof, Bezerkproof & Auto-Med armour on some blank Tetra's, it's the cheap man's ribbon but it works (Stoneproff for the Demonoliths who have the capability to Petrify everyone with their breath).
every standard monster is a walkover to me now, but i do remember when they werent & the right armour was a savior. But buuild up cash & Bribe Chimera Brain's for Lvl 4's And overkill Defewnders for Lvl 3's, I believe the Defenders in Zanarkand drop them rarely too.