Pros
- Your clear speeds are much faster
- You're not as reliant as your ult
- Late game your ult does almost 800 Damage
- You abuse your passive through FF stacks and high damage
- Assassin Damage with moderate Tankiness
- Scales really well into late game due to FF and passive

Cons
- Not that tank Jarvan people are used to
- Bad if your team needs a tank
- No lolygagging around, gank or farm in the jungle hard

I'll explain why this can work if done correctly here and how to do it.

First off, Feral Flare is an extremely strong item on certain junglers, mostly hos who auto attack a lot. Now most Jarvan's are just tanks that ult and do some damage. This Jarvan is a off tank with high sustained damage output. His 1st auto on someone due to his passive will deal 10% of their current health in additional damage so lets do some math.

Example A: Enemy A has 1400 health at the start of the gank, so you're guaranteed to do 14 extra damage to them. Plus Feral flare stacks, lets go with 10 stacks, which equals 10+25= 35 extra damage. So with those two combined, 35+140=175 extra damage on the first attack. Sounds mediocre right, not until we ad your current AD; lets go with 200. Including 26% lowered armor, and 5% pen from cleaver amounting to 31% armor removal. 200+175=375, 375*1.31 to include the armor pen and you have 491(before resistance after pen).

The majority of the reason why this can be strong is it abuses your passives and auto attacks. With those items you can hit 280 AD and abuse your already strong armor pen Q, and Martial Cadence along with having insane attack speed bordering 1.5 AA's per second.

Late Game - Now this is where you shouldn't be because you dominate early to mid with power. But in late game you're much stronger than they expect. With the AD scaling on your ult, it maxes at base 450, but +1.5 per bonus AD is amazing scaling. If your bonus AD is 180, that's 180*1.5%= 270. Now lets see how much you hit that ADC(1800 health) for with your ult, 450+270= 670 damage in one button. With 20 FF stacks(45), 31% armor pen, 280 AD, 10% of their current health(113) totals to 573. With just q and ult, you have the potential damage of 573+670= 1263. That's well past half their health.

That's the math of why it works.