should i buy pk with shards or should i up my heroes skill.my heroes are:
pd 7,druid 4,grimfiend 5, death knight 5,immortap 6
Those can't be the only heroes you have, OP. But, out of the ones you listed, PD and Grim could use shards. PK is decent hero, but he is not essential to you yet. And, he is relatively common legend roll. And, as Max said, bazaar is best way to get your first PK.
Agree with Fe203.
Immortep and death knight are not that important once you get more heros.
I would work on leveling up PD, Grim, and druid.
Also work on getting more of the LHC from daily reward or from warehouse to get a Cupid.
Once you get that, work on getting PD and cupid to level 7 first.
This will help you clear more dungeons which is great for getting resource.
PK is a great hero but at ur stage it won't help much.
No shards you ever spend on PD won't be worth it, almost no shards you spend on grimfiend won't be worth it, and most shards you spend on druid will be worth it.
If you never have a good death knight or immo, it won't matter in the long run.
Until you get Vlad, though, I'd keep Immo up to speed with all of the rest of your heroes. And I'd prioritize PD and grim. Druid can get by on 7/10 for a very very long time.
PK is good and worth having, especially if you can get scatter on him. I would try to see if I could roll him first, if I were you, or buy him in the bazaar for a buck. Or ... maybe you'll roll somebody else just as good or better while you wait. There are a lot of great heroes released lately, most of whom you would probably like more than PK.