Finns have brought up two questions and I'm not totally certain how the situations would resolve. Here are the 2 questions:

1) Player A has Gamiratar on his hand and Kyrstronand Propeller Mutant in the battle zone. Player B uses Invincible Abyss and Kyrstron and Propeller gets distroyed and their abilities triggered. Player A decides to activate Kyrstron's ability first and puts Gamiratar into the battle zone and it's ability is now also getting triggered. So this is where the question occurs: Can player A choose to activate Gamiratar's ability before activating Propeller Mutant's ability or is he forced to use Propeller Mutant's ability first since it actually was triggered before but wasn't just yet used?

2) The other question is much simpler: If I choose Human race with Petrova's ability, does it also boost Human Baku raced creatures? Petrova's Ruling wiki page just mentions that you can't choose groups of races but Human isn't really a group of races. Also Human Baku's wiki page states: "Human Baku are affected by all cards that affect Humans, but currently there are no cards or evolution creatures that specify Human Baku."

1) This should count under the Rule 5 of the Trigger Ability page. After Kryston has resolved and Gami is in the battle zone, you are left with the Gami and Propeller Mutant to resolve in the order you like.
*Note: I guess it depends on whether you know their hand or not, but wouldn't you generally want to discard their hand by the Propeller Mutant in hopes of hitting the creature?
2) Yes. As the support section says, every Human Baku is a "Human", and gets any support (as well as being able to be evolved from) that any Human could. Therefore, Petrova picking Human gives power to both Human and Human Baku.  
*However, the reverse is not true. If you picked Human Baku by petrova, Human's would get no race.

Thanks for your guick replies.

That's what I guessed and you are right, generally you really just would want to discard first but there could be some rare occasions you wouldn't want to do that. The example could have been a bit different but at least you got the point.

That's an interesting ruling Petrova and sounds logical, although I could have seen this resolving other way. I have a minor follow-up question. If Dragon race would ever be created, would I be able to choose it and thus boost all Dragon creatures in the battle zone. At the current state it is not possible since Dragon is counted to be a group of races and not a race. I'm just curious and it's okay if this question can't be answered.

Thats ok, I dont mind hypothetical as long as its never too crazy.

If there was ever to be a Dragon (or Cyber/Command/Monster) as a standalone race on a card, then yes, once its considered an actual race, then you can choose it with Petrova.

Okay, thank you Yami Michael for these clarifications!