ifonly

Then why even make the deck?! It doesn't make any sense!
The deck is literally shit and has no winning strategy to it, whatsoever.

Nope. I play in person. Life totals are 20 and its rare to see them get any higher than that.

And how often are you able to pull off that combo?

That's fine. How are you gaining life for archangel of thune?

Welp... nevermind then I guess.

This is an illusion deck with a whopping total of 2 illusions. You have dismiss into dream, but that doesn't make your things illusions, only others.
Fun fact, there are actually good illusions out there, and they can destroy this deck without problems. For instance, Dismiss into Dream is used much better with a Krovikan Mist.
Also, no idea why Consecrated Sphinx is in this deck. So you can draw more cards? You could just add like a howling mine or divination or something. Way cheaper.

You should throw a soul warden or soul attendant into the deck. Your creatures will be huge in no time if you have out Archangel of Thune and Soul Warden on the field.
Also, I don't really see the point of thousand year elixir. Is it so that you can use Thraben Doomsayer's or Beguiler of Wills' ability faster? If so, that's kinda boring. Just throw in protection spells or indestructible spells in there for those guys and wait for you turn to come back around.

Thrumming Stone. Shadowborn Apostle. Game.

Lilliana's Caress for starters.
You say it's a kill deck, but where's the kill spells? I see a sacrifice spell, but that's only for you. Where's the control? Where's the winning strategy? How does the deck actually win games?
Do you just make them discard and hope you deal enough damage while they have no cards in hand to actually win you the game? Or is there something I'm not quite seeing right now?

Add more mill to the deck, and more creature removal. Jace's Erasure is a good start. You're going to get stomped if you play this deck and not have much for creature removal or cheaper spells.
The only way I can think of this deck actually working is if your opponents are passive and just let you do this to them.

So for starters. Lets make hydras actually the focus of this deck, instead of elves. You could take out all the arbor elves and elvish visionaries. Replace them with Llanowar Elves and more hydras. Surprisingly enough, there are some actually good ones out there. You've already found two of the best ones. Keep looking. The doubling counters thing will make this deck unstoppable. Especially if you gave them all trample. Jesus Christ would this deck rape then. Since you have so many elves, maybe Immaculate Magistrate could help out with the counters.
Speaking of counters. Isn't that a huge focus with hydra decks? Aren't you supposed to use counters to power them up or something? Shouldn't some counter movement cards or counter addition cards be added to the deck so that you can quickly boost your creatures?
But anyway... Your deck. Do as you please.

What I'm seeing is a hope that you pull Craterhoof Behemoth late game and make all of your creatures attack and overpower the enemy.
Am I wrong?
If you're wanting to use Kalonian Hydra to the best of it's abilities, I would A) suggest many more hydra cards or cards that use +1/+1 counters, like scute mob or primordial hydra B) focus less on the draw power of your walls/spells and more on the moving or addition of +1/+1 counters.
Also, sideboarding some enchantment or artifact removal would help you immensely.
Your deck. Do as you please.

Decks like these always seem to just sit there, building up life, hoping that no one will just utterly destroy them, or mill them out before they can pull their combos off.
If I seem to be acting rudely, I apologize, but this deck doesn't really have a backup plan or a real finisher. You have Felidar Sovereign. Great. Getting your life total up to 40 or higher. Seems easy? Can be a lot harder than you think.
All of your flying defense has been side boarded and is pretty costly. Your sideboard is usually made for removal, yet you have a single defy death, and two more wrath of gods? Really?
You have an enchantment that'll help you as long as your life total remains high. If you're fighting a burn deck, you're screwed. If you're fighting a mill deck, you have a chance with the elixirs, but how often do you think you can pull them?
Green will trample over you, and you can't really stop it with the small creatures you have. Consider Chastise to combat this.
Path to Exile or Sword of the Plowshares could greatly improve this deck.
Also, don't sideboard a 5/5 flyer with lifelink, first strike, and pro demons and dragons. That card should always be mainboarded.
My last little rant is on Lapse of Certainty. I personally hate that card. You've delayed someone for a single turn. Congratulations.
Sorry for my rant. Your deck. Do as you please.

Yeah.
Didn't know you were going for standard. Sorry about the non-standard recommendations then.

This deck would be most used in multiplayer, so Stalked Prey wouldn't help me all that much and would help my opponents as well. The deck was meant to be quick enough to kill if needed, but durable enough to withstand attacks against me as well.
You're recommendations are good, and I will be using some of them, like Terminate and maybe Sign in Blood. I was trying to avoid random burn damage as that hasn't been too effective in the past.
Thank you for the advice.

What would you recommend I replace Nocturnus with? I liked his +2/+1 and flying boost.

Ah. I should've guessed that with a name like "Standard Sac Deck". Maybe Undying Evil then? Just to keep certain creatures alive for a longer time?

This is just me, but I'd run 2 vorapedes, 3 pyreheart wolf, 2 hound of griselbrand, and 3 ooze flux.
You could put in 4 blood artist and 2 grave pact. Should be all you need for the deck.

Ah. I see. I got mixed up on what set Seasoned Marshal came out in. But the lands could still use a balance.

Then I hope I have some curses on them or something to boost the damage they'd take.