Intro

Gods Unchained has been revealing spoiler cards from the new expansion (currently untitled). The new set brings new keywords, and the effect of the new keywords has not been revealed yet but we can make guesses at what they do. The pictures include all spoiled cards with the relevant keywords up until this post is published. All spoiled cards revealed so far are posted in @copperpitch's discord Copper's Crypto Clubhouse.

Echo

All the echo creatures have a ghost copy of the creature in the artwork, so echo has something to do with getting a copy of the creature. The legendary creatures have a ghost of another character related to the legendary, e.g. Dalia has her ghost husband, instead being a ghost copy of the creature but I think that is about card flavor and lore rather than legendries getting a different echo effect.

Initially, I thought it was going to be the same as Hearthstone Echo where the card can be played multiple times in one turn by adding a new copy of the card to hand that goes away at the end of turn. This would let the creatures have more impact late game where you have the mana to play multiple copies. Although since it takes extra turns to unlock the higher mana playing multiple copies in one turn is a lot weaker than playing a single card with equivalent mana cost, 3 Bold Scholars don't stand up to Polyhymnia. It also doesn't fit with the ghost copy in the art.

Adding a copy of the creature with the same stats without echo pretty much turns all echo creatures into draw a creature, and would be too strong as every echo would be a +1 in card advantage.

After seeing more cards, echo looks like it adds a 1 mana 1/1 copy of the creature to hand. The 1/1 copy probably sticks around in hand. All the echo creatures have effects that would also be useful on a 1/1 body e.g. roars, spell boost, or a passive effect. For example, Blade Borrower's echo would be a 1 mana 1/1 with the same roar, so you can weaken another creature. I would guess that the echoed copy would have a card aura in hand like frenzy creatures do when frenzy is triggered.

I'm pretty sure that echo doesn't have anything to do with roars. Echo is a keyword so it has to show up on a lot of creatures and having multiple creatures on board that interact with roar is too strong or complicated. The artwork doesn't line up with roar effects either.

For reference, in Hearthstone doubling Battlecry (Roar in gu) effects are very rare. It is on Brann Bronzebeard a legendary creature, and the Shaman questline Corrupt the Waters which needs you to play 6 Battlecry creatures to get the Heart of Vir'naal Hero Power that doubles your battlecries this turn for 2 mana. So having echo trigger roars wouldn't fit in power level wise.

Empower

The empower cards have Empower X and an additional effect. I'm pretty confident this is going to be the same as Kicker from Magic the Gathering, where you can pay an optional additional cost to have an additional effect. So you could play Surpassing Blast at 1 mana to deal 2 damage or play it at 4 mana to deal 4 damage instead. This opens up more options when to play the card, either play it now or hold it to play the empower effect later. I think the empower UI is going to look like when you play a choose one card where you have two options to pick from.

The numbers on the cards line up with empower as an additional cost. Surpassing Blast does 2 damage at 1 mana similar to Ancient Text and Illuminate, and does 4 damage at 4 mana similar to Wyrmbreath. Pharaoh's Heirloom at 1 mana summons a 2/1 and at 3 mana summons an additional 3/2, so 5/3 totals stats at 3 mana which is on curve.

Tempt Fate

Tempt Fate is the vaguest sounding of the keywords revealed and could be anything. One dictionary definition of tempt fate is "do something that is risky or dangerous". This sounds like Tempt Fate is going to be a RNG-based mechanic like Confused and Blessed. Based on stat lines of revealed cards, it is likely to be a beneficial effect, e.g. Vulpine Collector is a 2 mana 3/2 with Confused and Tempt Fate compared to Black Jaguar a 2 mana 3/3 with Confused and Regen 1, so Tempt Fate has to compensate for Vulpine Collector weaker stats.

The Fox's Venture gives Tempt Fate to a creature in hand for 1 mana so Tempt Fate has to be a beneficial effect. There is no reason to have a 1 mana card that gives a debuff, so Tempt Fate has to be all upside. I think similar to Blessed, the possible outcomes of Tempt Fate are going to be beneficial for you or at least have a negligible effect at worst.

Bone Roller reveals the most about Tempt Fate so far. It is a 4 mana 3/3 Anubian with "Roar: Tempt fate and apply the result to each of your creatures". It looks like Tempt Fate is going to be some kind of buff to creatures, either stat change or gain a keyword similar to Adapt from Hearthstone, like gain +1 strength, gain +2/-2, or gain ward. I'm not certain if it is going to be a delve where you can pick or it's going to be randomly chosen for you but I am leaning on it being delve. Based on this points, I believe Tempt Fate is going to delve a stat buff for the creature on summon, like how Blessed delves an effect related to favor.

Corrupting Influence says "tempt fate then apply the buff", so Tempt Fate might be all positive effects, or there is an off-chance that Corrupting Influence will only give positive effects. It's strange that Bone Roller says "apply the result" while Corrupting Influence says "apply the buff", could there be a gameplay reason for this difference in card text or did the devs mess up and leave an inconsistence in card text.

Some of the Tempt Fate creatures have effects involving attacking e.g. Blitz, Confused, or "When this creature attacks", having Tempt Fate being a stat buff would synergise with this. For example, Valka's Foreguard has Blitz and Tempt Fate, so you could tempt fate to get +1 strength and kill a 4 health creature.