I've had many people suggest I replace the second bloodthirster with infinity edge pointing out that due to the crit increase it would increase my average attack damage. This is completely true, as a matter of fact even with full bloodthirster stacks the second bloodthirster doean't come close to making up for the damage the infinity adge would add (avg dmg 699 vs 524 with this build) The reason I build 2 bloodthirsters is because of thornmail. look at the magic resist and hit points above. With 699 average damage and only 20% life steel a tank with thornmail becomes impossible to fight, you bump that up to 40% lifesteal, and you can take anyone 1v1, and alot of people 1v2. Additionally staying alive in team fights is alot easier with the extra lifesteal. Tristana with this build has no problems doing damage. This build is there to keep you alive without much armor or HP, and to keep the other guy dead regardless of their defenses.