The ideal combo is to have Whirlwind of Thought on the field, mutate in/on Vadrok, Apex of Thunder, and loop the damage/buff spells while keeping card advantage. Otherwise the deck tries to be aggressive with spells to control the board somewhat, which would also combo with Sprite Dragon.
Still trying to balance the land base. I don't want to lean too much on Raugrin Triome since it comes into play tapped, and only a few cards need white mana. I am using more shock lands to fill the gaps like Hallowed Fountain and Sacred Foundry, so I still get my primary red/blue colors but confirm white too. I don't want to add too many though as the self damage can add up. Fabled Passage is useful since most of my white cards are not playable until turn 4, but I worry adding too many will cause me to lose tempo before turn 4 if I draw multiple in starting hands.
Unsummon can delay their tempo, then later I can combo over and over with Vadrok, Apex of Thunder and Lore Drakkis. Clearing the field to attack freely helps, while delaying them from attacking me unless they have haste and I couldn't cast on their turn. It also lets me bounce my creatures to avoid removal. I can also use it to re-mutate creatures, because if it is a mutated creature I will get them all back to my hand. Stern Dismissal does let me bounce enchantments, but it cannot target my own creatures.
Weenie decks with many 1 toughness creatures are tough. Since the deck is lean on creatures and most get mutated, it is hard to have defenders without sacrificing attacks. Blazing Volley is in the sideboard when I run into those decks.
I'm actually looking at dropping Pollywog Symbiote for more impactful cards. With the current mutate creatures the cost reduction only applies around half the time. When hard casting Vadrok, Apex of Thunder and when mutating Lore Drakkis there is no colorless cost to reduce. The draw+discard is nice, but hard to reliably trigger after the first few mutations.
I really like Whirlwind of Thought, but dropping on turn 4 with no follow up can mess with my tempo. Since the deck runs on cheaper cards, unless I get Anticipate I sometimes am out of steam before I can kick the combo off. I might replace a slot with more card draw or some way to tutor, or just drop it for something like Firemind's Research.
Considering the differences between Thrill of Possibility, Cathartic Reunion, and Anticipate. Normally I prefer to avoid cards that make you discard before drawing, in situations where you have no other cards in hand. For this deck though it can pull back/replay noncreature cards from the graveyard, and Blitz of the Thunder-Raptor specifically gets stronger with more in the graveyard.
Trying to stay away from counter spells since those would get wasted with Vadrok, Apex of Thunder, but could still be brought back with Lore Drakkis if I find I really need them vs burn spells.
