If you are new to this game or If you arent familiar to Pantheon then please do me a favor and Gtfo! cause this build isnt for Pantheon players that dont know what they are doing. I started expermenting with tank panth cause i always get players in my team that... i cant find a nice way of saying it they suck and as a hybrid you dont have to deppend on your teammates as much
cause u can both deal dmg and receive dmg

As you can see the only diffrence in those 2 builds are Force of nature and Thornmail.
in other words if they are a team with full AD then you should probly use the first build or if they have just ap champs then you should go with build nr2(Captain obvious).
NOTE: if their team is balanced then i would recommend the second build it easier to use and
most champs do magic dmg.

It's really important that when you are at champion selection that you tell them that ur going mid

Early game lvl 1-6:

Buy long sword and 1 health pot and start heading to mid lane, USE spear shot as OFTEN as you can. just keep on harrasing if ur doing it right then you can probly get first blood at lvl 2.
but if you dont get it right then you should probly wait untill lvl 4-5 for second gank try
when you run out of mana your enemy will think that your and easy target so dont be afraid of using clarity before lvl 6

Mid game lvl 6-11
as soon as you reach lvl 6 your gonne want to go back and buy sword of the occult and if you can afford buy boots to(wich u should if u have done it right). And here starts the fun part take a look at top/bot lane and see wich side is more aggressive or lower on health(from their side) you use ur ulti behind them doesnt matter if it hits or not just make sure they cant run away first ur teammates can see the green ring of savior and then your enemies can see the red ring of death just before u touch the ground you should activate your Aegis of Zeonia followed by heartseeker strike if they havent died by that(miracle) then use ur spear shot flash towards them and repeat combo W,E,Q (if your target doesnt die from that then take it as a sign from God that you shouldnt play LoL) the chanses of you getting both of them deppends on how good you did at mid lane, after that you should probly go back to mid lane and as soon as your ulti is upp again just repeat same thing, before you know it you have at least 14 stacks and the heartseeker strike skill will be dealing more then half your targets hp
Late game lvl 11-18
at this rate you should probly just stick with your team and in team fights try to be the initiator even with a noobish team you should probly be a hardcore carry that can handle dmg.

going to keep this short

I use clarity cause you need that mana early game to get fed
and i use flash so i can get in or out fast

and for the items, i stack bloodthirster for a reason, panths ulti has a long cooldown so you dont want to keep going back and fourth and with the life steal they give i usualy kill creeps to fill up my hp

English isnt my strong side so i apologize for that ^^
And please try the build out before you criticise it!