Hey.
The
flash hulk combo can be very powerful, so if you're looking to make this a combo deck, there are worse to choose.
The combo works by playing
flash, putting
Protean Hulk onto the battlefield then not paying to keep it
alive as per
flash's effect. You then sacrifice the hulk and make use of it's death trigger to go and find certain combo pieces. Exactly what pieces you find will depend on what colours you are running. There are loads of potential combos you can make use of. Here is a Reddit thread that outlines some of them and how they work:
https://www.reddit.com/r/CompetitiveEDH/comments/67czr7/protean_hulk_combos_by_color/If this is a route you want to go down, then I would highly recommend you familiarise yourself with what pieces you will look for, how they interact with each other (especially on the stack) and how they can be disrupted so you know the right time to use it and how it all works.
In terms of it's viability, it's akin to any combo in a singleton format. It's all about how reliably you can put it together. There are a reasonable amount of tutors that can help with this, but in Chulane's colours they can start to increase in price so this might be a consideration for you.
Mysical Tutor and
Worldly Tutor (which you already have) are probably the best options, but there are others too. I wont list them all here. A simple Scryfall search should show you everything you need.
In terms of what's missing from the deck, it's quite hard to tell.
When I first looked, I thought it was missing a ramp package, but when I looked a little close I noticed all the mana dorks (
Llanowar Elves etc.) which obviously play well into Chulane's ability. It would be really helpful if you could sort your deck into custom sections on the deckbuilder. Usually decks get split into things like Ramp, Card Draw, Removal, Combo, Lands etc.
Here's one of my decklists to show you what I mean:
https://deckstats.net/decks/132604/1331854-black-yahenni-voltronThis really helps show how much of each element of an EDH deck you have included and will help highlight any areas that could do with propping up or are excessive, but also gives us a huge
insight into why you put a card in the deck in the first place. Of course, most of the time this is obvious, but occasionally it's not so it's worth doing.
I hope this has helped and I hope you have fun with your deck, however it ends up.