Hearthpwn

Malegos is the kill combo in almost all longer games. Spell druids are a bit easier since you have so much board removal, and if you hold on to the double to minion damage minion, you can do huge clears as well.

Frizz is almost a core card in this deck. Even after getting tome, you can reduce Maligos to 7 mana instead if you would get to draw it normally and being able to get that extra spell in guarantees lethal. Also when using plot twist after you played the Frizz, all dragons in your hand that have been drawn through plot twist from your deck will cost 2 less mana. Zzeraku at 6 mana cost is also very strong as dropping it early and using Rain of fire or tapping to proc it can be a game changer.

There is in total 6 dragons in this deck, so even if you have one or two dragons in your hand when playing it you can get 6 or more mana reduction overall which is great value. A 5 4 stats for 4 mana isn't bad either which has to be dealt with, overall the card has a lot of value.

Yes

You get so much healing that it doesn't affect your health to much. Also hunter dragon decks and demon hunters output so much damage that 3 dps doesn't compare, if you don't get the proper cards you are dead vs them either way and a hellfire to clear board can save you a turn which you wouldn't have gotten without it.

Also hellfire is great as finisher as well when you draw it for 0 mana in combo with maligos which is essential vs many decks. The combo with Zzeraku is also great, as it summons an extra 6 6.

Portal is to slow and is only useful for late-game while other cards provide more synergy and are useful across all stages of the game.