Bottom #5: Flesh to Dust
I have no doubt that this will be seen in Limited, but it's going to be one of those cards that you don't want too many of because of how much it costs. Outside of Limited, the only decks it'll be run in are those made by new players who don't quite understand tempo or value.
Pros: Kills a dude, prevents regen
Cons: Costs 5, no additional effect
Bottom #4: Mass Calcify
I didn't like it when it first came out and I still don't like it now. One of the biggest problems in Standard right now is Elspeth, Sun's Champion and this doesn't deal with it. Control decks won't run it either since it blows up their nice guys. Also, it costs 7. The only place I see this in is a one-of in the sideboard of an Azorius control deck in case they're being raced by some weird non-white deck.
Cons: Doesn't kill white, costs 7
Bottom #3: Research Assistant
Merfolk Looter is a good card. Merfolk Looter with a toughness boost would be a better card. Merfolk Looter with a toughness boost that costs 4 to activate is a terrible card.
Pros: Merfolk Looter with a toughness boost
Cons: Merfolk Looter with a 4 mana activation cost
Bottom #2: Soul of Ravnica
It's 7 mana to maybe draw 5 cards on a somewhat blue-intensive card. So, to get maximum value out of this card, you have to play a card of a different colour each turn, tap out for this, drop another land on turn 7, then tap out again to fill up your hand. And while you're in Magic Christmas Land, you will draw a Nalathni Dragon, a Shichifukujin Dragon, and three Moxes.
Pros: Card draw
Cons: Expensive card draw, really requires multicoloured cards
Bottom #1: Carnivorous Moss-Beast
It costs seven to put a +1/+1 counter on this. SEVEN. I don't think I need to say anything outside of that.
Pros: Plant Elemental Beast
Cons: IT COSTS SEVEN TO GIVE IT A +1/+1 COUNTER
Best #5: Nissa, Worldwaker
Ain't gonna lie, I hate Nissa Revane. I know she's good in elf decks, but I think her scope was too narrow and I don't like her. WotC seems to have gotten the message and made this version as universal as possible. She may only come in with 3 counters (which is why she's not higher on the list), but in a mono-Green deck, she costs 1. Her other plus one creates a issue that demands an answer since 4/4 tramplers can be a problem. Her ult may not directly win you the game that turn, but unanswered it will.
Pros: Potential 1-cost walker, creates tramply problems
Cons: Best in mono-green, ult lets lands get wiped easily
Best #4: Sunblade Elf
Is this the harbinger of Naya zoo coming back into Standard? Maybe, maybe not, but it's still an awesome little creature. It's kind of like Wild Nacatl but less likely to be banned. The other nice thing about it is that it has a relevant ability in case of the game running late. A mass +1/+1 buff may not seem like much, but it's often going to leave you in a much better position in case of matched blockers.
Pros: Basically a 2/2 for 1, relevant late-game effect
Cons: Requires white, just a 2/2 for 1
Best #3: Polymorphist's Jest
This + Circle of Flame will be hilarious. This is going to be a great trick, especially if your opponent thinks they're swinging into a large, but weak field with their creatures. I also like the fact that it changes their colour, which will nullify anthems effect like Hall of Triumph.
Pros: Turns a field into frogs for a turn
Cons: Doesn't stop any additional pumps (such as +1/+1 counters)
Best #2: Radiant Fountain
Some of you may cry "foul" for me putting this seemingly "meh" card so high on the list, but I have my reasons. 2 life may not seem like much, but it's 10% of your initial health, so it's actually more than you think. It also comes into play untapped, which again, my not seem like much, but it keeps you on tempo and allows you to play out your curve nicely.For a land that comes in untapped and gives you an effect, is there anything else you can feasibly ask for?
Pros: Comes in untapped, gains 2 life
Cons: Doesn't produce coloured mana
Best #1: Aetherspouts
This is going to be a problem and I believe it will be a bigger issue than Cyclonic Rift for a lot of decks. Why? Well, Rift costs 7 to get the full effect, this costs 5. And while Rift hits everything, it also allows your opponent to replay everything. This doesn't. If I'm swinging in for lethal with 6 creatures, I don't want to be told that I'm going to either have to spend 6 turns getting all those creatures back or never seeing some of those creatures for probably the rest of the game. At least with Rift, I may be able to throw down a couple creatures in my second main phase to try and recover from this. The only weakness of this card is that it requires the creatures to be attacking, which is something that not all creatures do, but for your mana investment, this thing is amazing. Oh, and one more thing, notice the lack of targeting, meaning is eats through hexproof and shroud quite easily.
Pros: Tucks or tops all attacking creatures
Cons: Only hits attacking creatures
Runners-Up (Bad): Kird Chieftain, Blastfire Bolt, Vineweft
Runners-Up (Good): Ajani Steadfast, Garruk, Apex Predator; Military Intelligence