I was just wanting to try and get some advice on maybe what to add to my little boys collection. He just started playing with them. What he has right now came from MallofToys 

Rage Longinus 
Nightmare Longinus 
Brave Valkyrie 
Judgement joker
King Helios
Lucifer the end
B-155 diablos
B-172 I think world spriggan
Super Hyperion 

And a few more I can’t remember right off. What could he add to get better pieces or beys all together Incase he gets into the competition side of it. I’ve tried watching YouTube and reading trying to learn more and more to help him I’ve gained interest in it myself lol.

I assume you're into Burst Standard.
To start off, you should read the rules for Burst Standard (from WBO) so you don't do illegal things, and don't illegally modify parts.
For buys, you should buy Guilty Longinus Karma Metal Destroy -2, the Astral Spriggan Customise Set and (when it releases) the SP Special Booster Set.
Since you bought Nightmare Longinus, I'll just suggest some buys for Limited.
the Cho-Z Triple Booster Set, Drain Fafnir 8 Nothing, the B-111 Random Booster Vol.10 FULL SET and Geist Fafnir 8' Absorb.

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By the way,
Burst Standard means the format where most released beyblade burst parts are legal. As of now, all are legal.
Burst Limited is the format when certain beys are allowed, comprising mostly of the God system and a few Cho-Z parts.

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People can you stop posting combos for testing if they are horrible combos (e.g. Burst Limited: Killer Deathscyther 6 Fusion)? Thank you. 
When will TT make Iron'...
I NEED IT