Hi thanks for checking my guide out, I'll give you some useful tips to play Jarvan as an Offtank Carry. I enjoy playing him as an offtank rather than a full fledged tank just because I feel that kills can make the game early on and Jarvan has some serious poke.

Mark of Desolation - I use these because his spear reduces armor and I feel almost all AD champs should use these marks.

Seal of Clarity - I use these because a good Jarvan always disrupts team fights so you need to combo your Q and E and its always nice to not run out of mana.

Glyph of Focus - These help out so much CDR is always a good thing to have no matter what champ.

Quint of Desolation - I actually prefer these Quints over the Fortitude just because I play rather aggressive and armor pen is amazing

Quint of Fortitude - Always good to have extra health these are viable Quints I just prefer more damage.

I use 21/9/0 standard off tank masteries. Gives you more offensive capabilities and gives you some DEF and MR.

Just try out the build when i get the Altmas Impaler I usually sell the dorans blade and either pick up a Thornmail or FoN depending on the other teams AD/AP ratio

Max out your Q first E second just so you can harrass and have lower cooldowns on them, you can also try to put points in your W and E to make them more balanced but only after maxing Q first

THIS ULT IS AMAZING, trapping enemies is great I love when kids tower dive me and even if I die I ult at the last second and 9 times out of 10 you will take them down with you. Try not to use it till after a team fight when theyre weak and running just pounce on your prey simple enough. Ganking mid is also a must just knock them up and ult em!

Thanks for checking my build out being that it is my first one I hope it helps out, if you dont mind leave a comment with some feedback of what you think. Best of Luck..... DEMACIAAAAAA (had to throw that in)