Hearthpwn

"So what's the point? You're opponent cant see the minion. How does that help me?" Actually it helps A LOT. These types of minions come with the element of surprise, so your opponent can never be too sure what minion you played. These types of minions can vary with effect, but to keep the surprise element, they will only have effects that affect themselves, or your opponent once they hit it.

"So, if they can't see it, then how will they know its on the field?" All submerged minions look like this to both players:

You can buff it, give it effects, etc, but it will always look like a 0/0. The only exception to this is if it is given Stealth, Elusive, or Taunt. if given a trigger effect or deathrattle from cards like Infest and Power Word: Glory, or if it has Divine Shield, the icon will NOT appear. For the player that owns it, you can check on its current status by highlighting it with your mouse (or finger if on mobile). When it dies, it will then reveal itself to both players before destroying itself.

"Ok, so what kind of cards would have the Submerge mechanic?" In a realistic sense, all cards with Submerge would have at least 2 with the same mana cost, with one of them having to be a neutral card. This way, your opponent can never truly know what you played, similar to how secrets work. For now, some running examples are:

So as you can see, these cards are used for very sneaky purposes. Dealing burst damage upon death, tricking an enemy into trading into Divine Shield, or outright destroying a minion is just a taste of what this mechanic offers... 

 
Clarifications:
-Turn count includes enemy turns.
-Cannot be targeted by normal cards
-Has an indicator saying how many turns it has left
-When the turns run out it dies
-Trinket cards can be given extra turns with (+X)

An example of a fairly basic Trinket card is 'Ward of the Naru' or 'Ogre Idol'. They stay on the board for (X) amount of turns with impacting effects. Trinket cards can only be interacted with by certain cards; such as 'Elothir, Archdruid of Lore'.

slippery: takes (x) less combat damage equal to your murlocs

the keyword slippery is a murloc-based ability, the character who possessed the slippery ability takes (x) less damage from minion or weapon attack damage.

the number (x) is equal to the number of your murlocs on the battlefield (note: a murloc with slippery only counts other friendly murlocs). Note that damages through battlecries/deathrattles/spells are not reduced.

slipfin brawler: not a good 5 drop by its stats, but when you already filled the board with murlocs, it will become really strong.

tinyfin's toysword: a decent weapon for early removal, not that the slippery effect activates on your hero means you can remove threats without taking toomuch damage.

murky: a murloc that can really give your opponent a huge disadvantage, the +2 health as well as the slippery effects on murky itself suddenly makes your board really sturdy.

explanation: let's use the cards i designed to explain how does it works

for example, i have a grimscale oracle(1 mana 1/1 give all your murlocs +1 atk), a slipfin brawler, and a murloc tinyfin on the battlefield, opponent attacks with his water elementa; thus, the water elemental takes 6 dmg from my slipfin brawler, but my slipfin brawler only takes 1 dmg from the water elemental thanks to the slippery ability he possessed, with 2 additional murlocs on the battlefield, the slipfin brawler now only takes 1 dmg when attacked.

So here's my idea for this week:

And three card examples of how this keyword would work if in-game:

Keyword: Hold Back (x)
Effect: The number (x) goes down every time it's your turn again. When it hits (0), the effect on the card occurs. 
Reasoning: We can now attach great effects to minions without them losing a decent vanilla statline

Thoughts & sounds Card 1 Deathstalker

Thoughts & sounds Card 2 Crazed Innovator

Thoughts & sounds Card 3 Apprentice Teep

 I hope you like my designs. Personally, I like Deathstalker best, even though the card is pretty bad itself, I think it's design could be really fun, and deckbuilding made around it as well (I imagine many taunts, and Wee Spellstopper to come in handy). 

My submission above. The keyword here is:

[Rivalry - This card is immediately summoned from your hand after your opponent summons the appropriate minion from their hand] (after battlecry has been fully resolved if any)

The point of this mechanic is to create a tempo catch-up mechanism, while also add another layer of predicting what you opponent might have in their hand and have both player plays around it. Tbh this mechanic is kinda broken in a certain way, but it's very situational (as you see the cards above), and yet extremely effective when dealing with the targeted deck / card types, so they should excel as a meta tech cards.

Muffled - Your battlecries are suppressed for one turn.

First time submitting, so any kind of feedback appreciated.

New keyword:

Unchain: This effect triggers whenver the minion is brought into play without being played.

So, p.e. this will trigger with stuff like Barnes, Nzoth, Ressurect, Madam Goya, Deathlord, Shredder, etc

So, the main thing about Unchain is to create funky decks that works around that mechanic. From simple stuff like ressurect and/or nzoth to more complicated like barnes copying and shadowstepping him back and etc. The cards I've posted are kinda basic, and I do think that having cards that trigger when they aren't played can be a lot of fun. Look at silverware golem, sooo satisfying getting that and I find myself always trying to maximize my way of playing to get it out for free, and etc.

Even though my examples only contain 1 deathrattle. I do envision a LOT of those cards having deathrattle effects, if only to make the Unchain effect more accesible. Given though that priest's ressurect comes earlier, it needs a bit of care to not have that many neutral deathrattle minions with strong Unchain effects: Getting the extra value 3-4 times/card due to mutiple ressurects followed by nzoths will be kinda broken.

Edit: Fixed the formatting and changed Horde's deathrattle (the actual keyword remains the same). I don't think that rogue needed the extra card generation old deathrattle, he already has plenty of ways to produce copies of the same card, like shadowcaster or gang up and etc.

Reflex. : Minions with Reflex deal their damages first when they are attacked, and if the attacking minion is destroyed, they take no damage. However, they trade normally when they attack, and are still vulnerable to everything else (including Silence).

They can make good walls to protect against swarms of small minions when they have Taunt.

Health Shield is a second health stat but it can only exist on minions.  This health cannot be healed it's like the Warrior's armor Hero power but on the minions.

Gives you more reach, especially in aggro.

Example cards:

Inspire is my least favourite keyword, so I thought it could be more interesting by flipping it the other way around; dissuading the enemy from using their hero power. The enemy will think twice before summoning totems, getting armour, dealing damage, etc.  

Edit: Changed pic size

Basically, whenever you draw a card with Reckless or a card with Reckless is created in your hand, it is immediately played. While Mana costs are listed on the cards, you do not pay it. Since the card is specifically played, Battlecries do activate. Here's some examples of Reckless cards:

With Clumsy Shieldbearer, he eagerly runs into battle and then trips on a rock. The "sleep" effect that occurs when you summon a minion normally lasts two turns instead of one for him. Extremely useful for stopping aggro.

Heroic Leap pulls a minion out of your deck and immediately plays it. Obviously there is huge combo potential with this card, or as just a way to put a minion on the board quickly. Just don't pull a minion that already has Reckless! Then not only will you pay 5 mana for the spell but the minion's Reckless effect as well.

Unstable Magic is an example of a spell with Reckless. Who knows what the arcane energy will hit? Its a dangerous gamble, but it could pay off. You can also pull it off of things like Babbling Book and Ethereal Conjurer for that extra burst.

With Reckless, while you do gain an extreme bonus in being able to immediately play cards and use your mana on other things, between the drawbacks and the lack of control it makes for interesting deckbuilding and choices. There's also potential for really fascinating legendaries.

Edit: Changed card picture sizes

Keyword: Timewarp: (X) The minion returns to the field at the beginning of your (X) turn.

Spirit Tiger: When he dies, he will resummon at the start of your third turn following his death. So if he dies on your Turn 3, he will be summoned at the beginning of your Turn 6. 

Martial Arts Trainee: The turn you play him, he will timewarp off the field and be summoned two turns later. So if you play him turn 1, he will be summoned at the beginning of your Turn 3. 

Bosch Verigan: When you play him, he will timewarp a minion on the field, which will then be summoned at the start of your second turn after playing him. His effect is like a two turn sap that returns the minion to the field without your opponent paying the mana to summon the minion again. 

Imprison works like a freeze effect, but also silences the minions for the turn they're frozen.

Interactions:

* Imprison lasts the same length of time as freeze would. So if you attack with a friendly minion and imprison it, it will not be able to attack next turn.

* Buffs applied to Imprisoned targets are maintained after the Imprison wears off. For example, let's say you imprison a Keeper of Uldaman buffed by Blessing of Kings (7/8 --> 3/4) that is then buffed by a Blessing of Might (3/4 --> 6/4). When the Imprison wears off the Keeper will become a 10/8, maintaining both buffs.

* Freezing an imprisoned minion will not extend the length of an imprison.

* Silencing an imprisoned minion will remove the imprison and all buffs that were "silenced" by the imprison effect.

* Faceless Manipulator will gain buffs on an imprisoned minion, but will come into play imprisoned itself.

* Imprison can be used in spell form as well as being randomly targeted.

* A randomly targeted Imprison could unstealth minions such as a concealed Auctioneer, allowing other minions/spells to deal with them.

Possible Uses:

* Completely stops Ragnaros for a turn, which neither silence nor freeze can do alone.

* Deals with pesky deathrattles if you kill them immediately (e.g. Sylvanas, Highmanes). This will block N'Zoth from re-summoning them. Unearthed Raptor cannot copy the deathrattle of an imprisoned minion.

* Allows you to go around taunt for a turn, possibly setting up lethal with spells.

Itensify:  Do something at the end and start of each turn.

About this mechanic, if the minion be summoned by portals, direcly from your deck or hand (Y'shaarj, Alarm-o-Bot), it will executes it's mechanic normally. But of course, if summoned by Alarm-o-Bot, the effect will count when you finish your turn, since the minion was swamped after your turns ends.

With Other Effects:

Neutral Rare Card: 

Paladin Legendary Card: