CDR for more ulti.
Dont need much AP because not high AP ratio
Zhonya very important. If you use Crowstorm+ Zhonya's Hourglass in right time, you can change game.

Your ulti will do damage around 470 per sec ([ 325 + 329*0.45 ] based on this build. You can go more ap) at 18 which will continue 5 second, if you manage to hit all enemy team it will 2350 damage each one and 11750 damage total.

And if your teammates good enough to help you, you can ace enemy pretty fast.

You will be first target if you initiate. You should always Terrify AD Carry, then Reap, if enemy team focus you use Zhonya's Hourglass, else you can Bountiful Harvest. If they focus you and you use Drain anyway, you probably die.

All i need CDR and few AP

Initiate
When i play fiddle i usually don't get many kills. Because i'm usually one who initiate team fights. I don't like team fight that i didn't initiate. Well its seems odd but i'm doing it because players usually stay together in late game, and if initiation happened they may getting away from themselves.

If you one who initiate you will be very big damage source to all enemy team. This is my main purpose. Make lots of damage. I don't need kills.

If you don't wanna play like that you can always wait other players start initiation. This way you can get kills maybe pentakill. But this is just chance.

If i have a chance to give kills to other players in my team, i always give kills to them.
If i have enough CDR, i give blue somebody else.

Tower dive
Tower dive with ulti and fear somebody then start drain from champion that you feared. You can tank tower very long time. But your teammate should communicate with you. Else you may be fail.

Careful while diving into champion like Sivir, Nocturne, Morgana. They can block your Terrify. Or Gangplank. He can simply walk away from you.

I don't get upset after die, if i have succeed my ulti and combo.

Once time i get into fight alone to all enemy team at our tower. Well, after i ulti them, some of them start hitting me and others hit tower in confusion. I wait until i get low on HP. Then zhonya. I got killed after zhonya finished but i succeed to defend tower and get triple kill. But mind that i have succeed to ulti and enemy team get confused. You can call this as "luck"

Once time after ulti, they stunned me and killed me immediately. Couldn't even press zhonya.

Pressing zhonya in right time very hard thing. If you press to early you may can't deal much damage (They mail run away or kill you after zhonya). If you press late, well you die.

Best Scenario
You initiate with ulti
Feared dangerous ad carry
Sended silence
Enemy team focused you
You used your zhonya.
Your team get in fight.

You will damage with your ulti at least 2 second because zhonya. Which its gonna deal almost 950 damage. If you managed to fear and silence you are probably gonna live much more than 2 second.

Doesn't matter if you die. Because your ulti in CD now :D

Good Scenario
You initiate with ulti
Feared dangerous ad carry
Sended silence
Enemy team started running away
Do not use your zhonya
You succeded something. You pushed enemy to run away. They probably gonna run like cows that don't know where is it going. If your team good enough to catch them, that's it.

And if you succeed to fear somebody, drain it. And he is probably gonna die with your ulti+drain.

And you should chase enemy team (with flash or running) if you couldn't fear their ad carry.

Bad Scenario
You initiate with ulti
Aaand they push you away. Maybe Alistar maybe Lee Sin.

Just flash back into fight, and continue your combo.

Worst Scenario
While your ulti channeling enemy team cancel it.

If they cancel it because you are too close enemy team its really your fault. If not they are probably have wards and its basically your fault too. DO NOT LET ENEMY TEAM CANCEL YOU ULTI

You suck
Your team suck

Your ulti too far from enemy team
You forget use zhonya
You used zhonya in not good time
You let enemy team cancel your ulti
You feared tank, not carry
You ulti blindly (I can't forgive this one)
You are not using wards. (Always carry one ward for ulti positioning)
You are not communicating with your team

Remind yourself it's not gonna work any team combination.

Fiddle ulti works very good with Galio or Amumu ulti.

And if your team is not helping you, then go for kills, get last hits, don't initiate, don't tower dive.

I have seen that i have failed with my own play style. You can fail. But don't get angry, just change your style based on enemy team.

I have games that i got too many kills and games that i really really really sucked. I'm just an average player.