Strategy

This deck is built around the commander, Vadrok, Apex of Thunder. He is paramount to the entire deck's function. What's that? It's bad practice to build around the commander? Thanks for sharing.
As you may already know about Mutate, a mutated permanent (hereafter known as a merged permanent) receives its characteristics at the copy layer. Long story short, if you make a copy of a Pollywog Symbiote mutated with Vadrok, it has both the characteristics of Vadrok and Pollywog Symbiote.

Recurse, Reuse, Recycle

When you mutate Vadrok onto something (or something onto Vadrok), you will want to cast an instant/sorcery from your graveyard that copies the merged permanent. These include Three Steps Ahead (see Rules), Cackling Counterpart, Fated Infatuation, Mirage Mockery, Quasiduplicate, and Rootborn Defenses (see Rules). Be sure to not put Vadrok on top, for if you do, the legend rule will apply (unless _____ Goblin is a component).

After that, you can return Vadrok to your hand by any number of means, mutate him onto the copy you made, and voila: You now have a merged permanent with effectively two Vadroks on it! Any further mutate onto it will yield two Vadrok triggers in addition to any other present mutate triggers.

At this point, you can keep casting multiple noncreature spells from your graveyard while still making more copies of Vadrok. The win condition from here involves beating people to death with your token army, but you could try some more bombastic noncreature spells under three mana to recursively cast.

Splice

Obviously, I am a freak on a leash. I am a rat in a cage. I am a dog chasing cars. I am a man with nothing to lose. Creating an imbred clone army of Build-a-Bears is not merely enough to quench my insatiable thirst for the asinine.
I must not only mutate, but also splice.
Blessed Breath, Hundred-Talon Strike, Spiritual Visit, Consuming Vortex, Desperate Ritual, and Veil of Secrecy can be spliced onto ANY cast spell if you pay the toll. Seeing as the deck is built around recursive casting, doing this repeatedly is not far from impossible.

The strongest splice option to me is Veil of Secrecy. This card is my everything. Not only can it protect your creatures from spot removal (an overwhelming weakness of the deck, although shroud is very bothersome), but it can return your Vadrok-merged permanent to your hand as a cost; it cannot be stopped! Granted, the merged permanent has to be blue in color to return, which can make it restrictive. Be sure to find it whenever relevant off of Eerie Procession, Solve the Equation, or Merchant Scroll.

Deckbuilding Considerations

The grand weakness of building around a commander is the interaction people will throw at it. Once players know what you are up to with Vadrok, they will want to stop you from resolving him ever again.
Fortunately, Vadrok provides blue, making counterspells an easy inclusion. Teferi, Time Raveler is also effective and castable from Vadrok, which is silly might I add.

Suggested Choices

You can sacrifice your instant-speed interaction by playing Defense Grid.
The deck plays Reach Through Mists, Peer Through Depths, and Sift Through Sands. You could search for The Unspeakable if you really wanted to, but he is more frequently going to be a dead card in hand.
Kykar, Wind's Fury and General Ferrous Rokiric provide tokens to pair with Vadrok. Rokiric is human and Kykar is slower to push out, but each are great options on a budget.

Rules

Some things to bear in mind:

• If you cast Three Steps Ahead from Vadrok, you must pay the one or more modes; these are additional costs that must be payed.
• Likewise, any splicing you do will also need to be payed.
• When you cast a spell and splice onto it, you reveal all the cards you want to splice onto the spell simultaneously; therefore, you cannot splice the same card multiple times onto a spell.
• If the topmost component of a merged permanent is a token, the merged permanent is considered to be a token, and can therefore be hit with populate as a mechanic.