I'm a 2x Rank 1 and Master+ player specializing in high MMR Assassin & "flex" play, and have played HotS since first wave technical alpha testing. I now stream and youtube more casually.
My guides are like notebooks. I update them progressively based on what I learn and theorycraft. As such, this guide is a culmination of my experience, successes, and feedback.
YouTube: OCM Ragnaros is an interesting melee assassin that takes an interesting turn from the very AP driven melee assassins (such as Alarak) that we've seen recently. Much of his kit crosses the line between AP and AD, making him almost inherently hybrid with the ability to build a number of different, yet effective ways.
In this guide, I'll go over what I see as the meta, and why. As always, my guides are merely suggestion based on the successes I've had with any given hero. I will be updating this guide regularly and logging significant changes.
BALANCE PATCH 22.4: No major changes; needed nerfs were applied across the board to most of Ragnaros' kit. I still find Q build to be most effective, and E build to be interestingly strong in light of not being nerfed with this patch.
UPDATE: Hit 10 with Ragnaros! Q build going strong.
BUILD EDIT:Made changes to the primary "3rd Degree Burns" build to coincide not only with what I have been more frequently using at high MMR since the 22.4 patch, but what I believe better reflects meta gameplay after his nerfs.
I believe this to be the most "meta" build, for a number of reasons but we'll talk about one in particular. (Admittedly, it tilts me pretty hard that people still don't recognize this.)
Ragnaros is a melee assassin. Melee assassins benefit from being able to, you guessed it, perform at melee range. Even furthermore, melee assassins benefit immensely from self-sustain.
Ragnaros' self sustain comes from damage dealt by his Q. I'll give you a minute to think here why this build is meta.
Did you think about it? Here's the answer if you didn't get it: Building Rag's Q doesn't only mean increased melee potency, it means you stay alive longer. As with ALL melee assassins, staying alive means you deal damage, dealing damage means you're doing your job. This build allows for synchronized, consistent burst damage that will not only chunk enemies, but provide immense team fight damage and excellent self sustain.
The key to this build is understanding the work that needs to be done to see it to its full potential. Make sure you stay on top of your minion stacks and finish up the very easy 15 globes needed for your regen and resistance at 4.
It's also important to note that the level 20 tier on Ragnaros is very flexible and very situational, including this build. Submerge is a great mitigation option, the second charge of Lava Wave is awesome for team fighting and map control, and Heroic Difficulty is amazing for structure defense in the late game. I've found that on larger, 3-lane maps, the two charges of Wave performs extremely well, while on smaller skirmish based 2-lane maps, Submerge is great alongside Heroic Difficulty as a potential defensive pick.
Alternate versions of this build are available below. Notice talent changes for heavy CC teams, better wave clear, global soak value, and so on.
I'm going to come right out and say it, I hate this build. I HATE this build. It contradicts nearly every part of Rag's intended design and the fact that people find value in taking full builds worth of W talents makes me want to take a dump in someone's mailbox.
With that being said, IF FOR WHATEVER REASON you chose to build a potent MELEE ASSASSIN for easily-dodged range poke, here you go.
I really don't have much else to say about this. I don't recommend you use it, but... it's here I guess. You're better off taking specific talents like at 7 and 16. Not the whole thing.
As the name suggests, I'm not going to take responsibility for this build. I saw this build in action on HORSEPANTS' stream, and was actually surprised to see it do well in niche situations.
The benefits of this build come from making sure you have targets within your E, and ideally making sure that you're casting E on yourself rather than teammates. The damage and utility that comes off of self-casting is what really amplifies this build.
The build has decent damage, okay sustain, and can actually widdle a team away pretty handily with some seemingly lackluster consistent damage that will erode enemy teams.
Success with this build comes from well timed self-casting on your E, full use of your E's mobility, and timing cooldowns correctly.
I'm not going to call this build meta, but I will call it fun.