Actually, TF is essential to a rengar build. I too was hesitant to get it bc of the bonus mana, but after more thought, I realized how good of an item it was. The 125% bonus damage makes a ferocity infused Q do so much damage it isn't even funny. The extra tankiness is vital, and the AS gives him tower shredding ability. I used to try and find ways to avoid getting TF but getting phage for the health and the sheen for the proc, it seemed only sensible to build TF then. Also, TF is now a bit cheaper to get and with the Jungle buffs, much easier to get early game.

THANIAS OUT!!!!

^
OMG yes, I love it when bot lane panics and runs for the brush. especially if my team has it warded.

Bonetooth has it's uses, but you have to know when to buy it. On your second back take a look at your progression (levels, gold, and kda) compared to the other 9 players, especially the enemy jungler. If you have a significant lead in any category then Bonetooth is probably a good buy. If you are behind, then that 800 gold would be better spent on items that help you catch up.

Meh, not a bad argument, but I still like the item :3 I get it anyways. If that happens, you might as well just keep it for the occasional gank or two, and go back to farming. 800 gold doesn't set you too far back, especially as Rengar, with whom carrying the game is not as vital.

I would be curious to see how early you are actually able to complete the TF. I agree, that extra damage is really strong in the early game when most players are under 1000 health. The problem is, the sheen proc doesn't scale, so with every passing level it becomes less relevant. I crunched the numbers and for rengar, the sheen proc will add 159 bonus damage to your next basic attack at level 18. In that same period of time, Vayne will have gained 1411 total health without spending a single gold. If you want to look at it in terms of per level gains, Rengar gains +3 base AD per level. That means that the damage from TF proc is increasing by a mere 4.5 per level. Compare that to Vayne who gains an additional 83 health per level and TF doesn't look nearly as appealing.

Lol, you are completely ignoring the damage items you would buy >.< When you have, lets say 200 AD and you add that by 125% you would end up having an attack that does 250 BONUS damage, and on top of that, a fully charged Q makes your next attack do double damage, so that would be 200+400+250 damage right there. (That's ignoring armor and stuff)
Idk bout you, but I think 850 damage is pretty nice for an opening attack.

Edit: That would be 200+200+250 lol, still 650 damage is pretty good too :P That's just one basic attack used with an ablity that can combo into a second attack to do slightly less damage then that.

I think you misunderstand how Sheen ( and by extension TF) works. That 150% does NOT use your total AD. It's caculated based purely off your BASE AD (the AD you start with + what you gain each level). So the actual value of the Bonus damage would be 159
(55 starting AD + 51 AD from levels) * 1.5. AFAIK since it's bonus damage, it simply gets tacked on after your base attacks and abilities, it doesn't actually increase them. So will a full ferocity Q you are actually doing

(106 base AD + x Bonus AD + 150 Q damage) * 100% if crit + ((106 base AD + x Bonus AD) *100%) Ferocity Bonus + 159 sheen proc.

With no items and no crit the total is 256 + 212 + 159 = 627
With no items and a crit the total is 512 + 212 + 159 = 883

Figured that out after typing my response lol. But still, it is a good bit of damage to add to his burst, and it gives him health and AS and crit chance. So I still like it.

If you are interested I did some additional math to see just what the actual value of that sheen proc is. At level 18, with full ferrocity and no crit, the bonus damage from sheen is equivalent to 53 Bonus AD. In other words, adding 53 AD via runes and items increases your total damage from Q by the same amount as proccing TF.

53 AD is worth 2120 gold. Looks like TF may actually be more useful than I thought.

my matchhistory tells u how to rengar

Rengar sucks. Refund now.