This petal build is meant to be the standard for petal. Any build that gives you anything less should be ignored. This is my personal petal build and coupled with good teamwork and game sense, this build has great potential.

Where to start, maximizing petal's potential can be difficult. If not played well, petal can easily be dead weight as she is very squishy and without the proper items she has generally a low damage output.
(Try making a vanilla saw face a vanilla petal and you'll see what I mean.)

That being said, with the right build and play style, she can easily win 2v1s from early to mid game and occasionally in the end game.

Play style is very important with petal. More important than the build actually, so that's shy I'm going to go over the playstyle first.

When learning petal, the first thing that you need to know is how to leash your minions, as they are roughly half of your damage output for a good portion of the game.

Petal's munions only chase after opponents when your character starts their auto attack animation. So even though your munions could theoretically reach them, if they are out of your basic attack range, then you won't be able to sick them on your opponents. But as soon as your character shoots their first basic attack, your munions will run past you in pursuit. This takes some practice but it is crucial to playing petal to her potential.

Petal's munions also count as crystal damages. This means that frostburn and eve of harvest will work off of munion damage. However, the crystal life steal from munion attacks is negligible, almost irrelevant in most team fights so it's not recommended, especially not over frostburn or other attack items.

Frostburn is essential for all petal builds. Period. There are too many uses for it to leave it out of a build. The reason frostburn is so important is because it enables both pursuit options and escape options. And not dying is always a priority.
How frostburn works with petal is with her munions. Her munions count as crystal damage, so they will slow down enemy heros as soon as they hit.(does not work on minions or the kraken.)
So if another enemy hero is chasing you, all you have to do to get away is get that first auto attack off and your munions will pursue and cover your escape. The same works in reverse. When your opponent tries to run, as long as they are within your basic attack range, your munions will pursue and slow the enemy.

This means that baiting and kiting are essential tactics for petal since you have every advantage over your opponent when they are chasing you(numbers matter though, so if it's three on one then you should probably just burn your boots and get out.

Another essential thing to know for petal is how to jungle. The game says that petal is a laner. But petal, if used correctly, has a jungle clear speed comparable or faster than Koshka. This is because petal doesn't have to stop moving to deal damage. This works off of her munions, if you get the first basic attack off. Your munions will continue attacking the jungle minion until you are out of a certain range from the munion. This takes some practice but with some time you can clear both sides of a jungle in under a minute. That's right, less than 60 seconds. Note that frostburn does not slow minions like it does heros.

Although the following strategies are really basic vainglory strategies, they are still necessary for petal. The first thing is: never engage an enemy without a purpose. In the early game, jungle minions are actually worth more than ganks. So in the beginning, if you feel you can scare off their junglers from their own jungle, then you will be both increasing your own money gains as well as stunting your enemies growth. Note that just because petal is strong in the early game, she's not invincible, so having a reliable escape or backup is essential.(frostburn...other junglers on your team, boots,etc)

Counter building your defense is also extremely important with petal as she is very squishy and needs all the help she can get. Don't wait to start counter building your defense, because not dying has the most synergy with being alive lol. Sometimes I start counter building even before big teamfights erupt.

End game strats...

Honestly, the only consistent thing I can tell you is to keep your team together, you are always stronger with your teammates. Too many games have been lost because someone wanted to take a minion mine alone. Stay with your teammates pretty much always.
Other than that. The end game has so many variables that strategies won't ALWAYS work. This is where game sense and experience take over. Don't be over zealous with your play. It's almost always better to retreat and fight again later than to put the rest of your team in a 2v3 situation if you die.

With that, good luck. I can't think of anything else to say on tactics technical skills or strategies.
Onto the build.

This build is meant to be the standard and what I think suits the most situations, so feel free to tinker around with this yourself.

There are really only five things that are essential for this build. Other things can help, but honestly, we usually win before I can even finish this much so while there are other things that could maximize, those situations are rare. And consumabLe items start becoming more useful at that point.

So for your early game, the first thing you need to do is start working towards frostburn. This build is a little different because you go straight for a tier three, don't be alarmed. That passive skill is really that important and its relatively cheap for a tier three so you should absolutely have it by around 4 5 or 6. Just jungle or lane as fast as you can and get it as soon as possible because it will be more reliable than boots or more health many times in escapes. ^^^(strats)

Then after you have frostburn, work towards level 2 boots since they will help you clear jungles and escape even faster. Journey boots are not required and will just set you back 900 gold from more important things.

Now you could either start working on sorrow blade, tornado trigger, or shiversteel. There's not really a specific order and it becomes situational on what needs to come first. If you need more damage and you're not being hurt that much, go for sorrowblade or tornado trigger. If you are having trouble staying alive, the work on shiversteel.

Now to explain these items. While sorrowblade and tornado trigger may seem self explainatory, it's imprtant to remember that any and every build needs to be centered around MAXIMIZING your potential. So while having tyrants monacle is better than not having tyrants monacle, there may be something better you could do with that money.
Sorrowblade and tornado trigger just give you better damage, plain and simple. You don't have to worry about stacks, crits, or anything else. Petal is pretty complex so there's bo need to make it more difficult than it needs to be. Plus I honestly couldn't find any combinations that were any better in time to kill.

Now shiversteel is where it gets tricky. Shiversteel is meant to be used like frost burn. On command it slows down your enemies, while giving you an extra 600 health to boot. Shiversteel is a more aggressive and cheap alternative to crucible. Though if you are really hurting for health (you need to retreat more offer and work on your counter build) then crucible might be better for you, at that higher price tag though.

Other than that. You just need to counter build your defense. Counter building your defense just means that you build defense items that block what your enemy's primary damage dealer is attacking you with. Meaning that if they have a saw with three clock works and three shatterglass. You should probably get an aegis (not a suggestion, do it or you'll regret it)
Also know that this is the one thing that isn't in chrinological order, as soon as you get frostburn and level one boots you should start thinking about your counter build. It's never too early.

In conclusion. Petal is very strong. Don't be afraid to change something on this build. Go practice, learn how to use your munions. The end. Game sense and experience are hard counters to a good build haha

I didn't comment on the threats section because every character could be a threat in some way or another, and there's always a chance when pubbing that you'll face someone either incredibly good or incredibly bad regardless of their build or their character. I've seen Catherine's that can take down saws and adagios that can take down glaves. Judge them by their skill. Not their character.

I also left the abilites section blank because it's so situational it's not even funny. Do whatever you need. If you need more overall damage. Go skill b. If you need more health regen. Go skill a. If you need something for teamfights. Go skill c (just remember to save it for special occasions because that cool down is not forgiving.)

If you have a question then you should probably figure it out yourself because I learned most of this in private matches with a friend just testing petal. I don't have any inside source in super evil megacorp.
And I don't think I'm super committed to responding to everything. But don't get sad, I'm just frustrated because this was a beast to write. This was hours of research and testing. I honestly don't know if I'll ever do one of these again because this took so freaking long.