Similar to the other spiteful decks in the past and present, Spiteful mage uses board control to set up our win condition of using alexstraza/pyro as a finisher.
Dragon synergy is used because of how strong of a card scaleworm can be in the current meta. It also lets us get further value out of having alex in hand and taking advantage of cobalt scalebane with board control. Primordial drake battlecry is another great tool in a deck not running many spells.
An interesting thing to note is how this deck uses nightmare amalgam. Not only does it give us a dragon in hand, but it also counts as an elemental on board. So if you end up using frost lich jaina in longer matchups, tar creeper/arcane tyrant/fire fly/ and nightmare amalgam can offer us healing to stall until lethal.
This deck is overloaded with taunts to help get us to our spiteful summoner swing turn/stall for a pyro finish.
Lastly, we can cheat out arcane tyrants with flamestrike. Since this deck is all about board control, turn 7 flamestrike into one or two arcane tyrants with a board already in tact can be a really game deciding turn.