This is going to be playable in aggro – King Llane is one card that gets out of your deck entirely so you only have a 29 card deck, and aggro loves that (the part where Patches removes itself from your deck is one of the reasons why that card is so good), while The Kingslayers is a Fiery War Axe that also draws you a card on each swing. Granted, it does draw one for the opponent as well, but most Legendaries are expensive and if you kill the opponent before they have enough mana to afford to play theirs (which, as aggro, is what you’re trying to do anyway) the fact you drew it for them doesn’t matter.

Garona Halforcen herself isn’t that impressive because relying on your opponent to have a specific single card in their hand that never starts in their opening hand to get the effect is not going to work often, particularly since the opponent can get rid of it, but at the same time, the THREAT of her existing encourages the opponent to pay 3 whole mana for an effect only worth 1 mana, since playing King Llane largely has the same effect as trading a Tradeable card – and making the opponent repeatedly waste mana trying to avoid the effect of a card you might not even draw is quite good for aggro.

I think S’theno is a 4-star generic Midrange card.
It is Immune while attacking on ALL attacks, not just ones triggered by spells, so Aggro decks ignore it at their peril (peril of losing the board and being unable to get it back) even without spells in hand to back it up.

She is also decent against Control/Combo decks because the triggered effect when you play a spell does NOT specify “enemy minion”, only “enemy”, and can thus go face – stack this with the number of cheap spells DH has that gain attack or draw cards and this can really help find the last little bit of reach to get lethal against opponents with no board or high health minions – particularly notable against Druid and Warrior because Armour is not Health and thus doesn’t prevent S’theno going face.

The final thing to note is that 4 health on a 3-drop is quite solid, and playing her on turn 3 into an empty board is real good, because developing into her is really risky and removing her isn’t easy for several classes (particular note – a lot of removal only does 3 damage, which isn’t enough on its own).