Hearthpwn

Underdog: Its a keyword that reads "if this minion kills another one and survive, transform it into its legendary form". all underdog cards have normal rarity and are fairly weak, but become legendary if destroy one creature. If you have 2 copies of the same underdog creature, only one can become its legendary form during the game.

Defiant crusader turns into...

Elementalist of the ring turns into...

Next: Barbed.

Barbed X means whenever the minion or your hero (if it's on a weapon) is attacked, it deals X damage to the attacker before taking damage.

Next: Courage/Courageous

Quote from nurgling13 >>

Next Keyword: Regenerate/Regeneration

 Regenerate (X): Whenever a card Regenerates for example, (2) it fills 2 mana crystals this turn. One card for every class.

Wander X is a minion keyword that means it won't be summoned until the beginning of your turn, X turns after you played it. A minion with Wander 1 will be summoned at the start of your next turn. Minions with wander still have summoning sickness unless they also have charge. The idea is you can cast for cheaper, but it gives your opponent time to prepare - they see the card when you play it. (Remember that it also means on the turn it's summoned, it's being summoned for 0 cost, so you have plenty of synergy options.)

(Note: these cards might not have the best balance, this mechanic seems very sensitive so I erred towards unplayable rather than gamebreaking. Suddenly I have lots of ideas for cards with this mechanic; I skipped some more obvious ones, like Lost Adventurer, in favor of these 3. Oh and, yes, this is based on that one mechanic from MTG, I can't remember what it was called, with the Time Counters.)

Next Keyword: Endurance

Edit: OH! like Battlecry, Wander won't activate if the minion is played directly from your deck, or summoned from something like Summoning Stone. I don't know of any way this could happen at the moment, but if it is somehow played from your hand on your opponent's turn, then Wander won't activate.

Eifhr

Quote from nurgling13 >>

Quote from kittlish >>

I don't know of any way this could happen at the moment, but if it is somehow played from your hand on your opponent's turn, then Wander won't activate.

Ancestor's Call can do that.

Endurance is a keyword for Ice Block like effect but on a minion. So when a minion would died when taking a fatal damage, prevent it and the minion become immune this turn only, but a turn after Endurance trigger kill the minion regardless of its Health.

Next Keyword : Ritual

Quote from GearOFF >>

 

Next Keyword : Ritual

  

Leech: When this minion kills a minion do X.

Ghoul is a vanilla 2/1. An alternate idea I had would be to make cards like Mistress of Pain have their effect be the Leech keyword.

Next Keyword: Madness

Dismantle is something that can only happen to mechs, and when it does happen, it destroys the minion and spreads it's stats randomly among ALL other minions.

Next Keyword: Unbroken

Unbroken: Can't be killed in combat. 

So essentially these minions must be dealt with abilities/spells/hero powers, things like Unstable Ghoul, mage hero power, Arcane Missiles.

Next: Benevolence

Explosive: when damaged by a minion there is a 50% chance to destroy both minions.

Next word: Trample.

Oblivion is a keyword that activates if (X) minions have died during the current game.

Next: Radiate 

Quote from Enchirideon >>

This perhaps may seem off topic, but I have compiled all the abilities that seemed to most fit within the game UI and flow that we currently have into one place. I just wanted to. Any abilities not mentioned were either duplicates(there were a few), can be easily expressed with other keywords or are simply too complicated... or I just missed them. I tried my best to make them as dynamic and understandable as possible, with the possibility of sticking them on anything as "this" can be a weapon or a minion or a spell as well. Enjoy the list:

Train: Return this to your deck, give it +1/+1
Scout X: Look at top X cards of owners deck, draw one and reshufle the rest.
Timewalk: Do the following if owner played no cards during the previous turn.
Berzerk: Do the following whenever this takes damage.
Honor X: Do the following whenever you summon a minion with a cost of X or higher.
Feast: Do the following whenever a minion dies.
Upgrade: Do the following whenever a spare part is used on this.
Fear: Do the following whenever this is attacked by a minion that costs more.
Avenge: Do the following whenever a friendly minion dies.
Resonate X: Do the following whenever you opponent plays a card with X mana cost.
Meditate: Do the following if this did not attack this turn. Does not come into effect the turn it is introduced.
Rebirth: Do the following if owner has already played this card before.
Arcane: Whenever you cast a spell, do the following.
Mmrrggl: Do the following whenever a murloc is summoned.
Toxicity: The attack of this scales with spell power.
Doom: This grants the following to anything it attacks.
Transparent: This is shown to all players when drawn.
Bribe X: After playing this, do the following if you have X mana or more left and spend X mana.
Duel: Do the following after this kills a minion.
Sleep: This is disabled until it is damaged or becomes the target of a spell.
Cursed X: This deals X damage to owner at the end of owners turn.
Cleanse: return a minion to it's original state, as though it had just been summoned.
Betray: This changes sides and owners if the following is true.
Dodge X: Whenever damage is dealt to this, reduce it by X.
Fuse X: Do the following X turns after this comes into play if this still is in play.
Flee: reshuffle this into your deck
Sacrifice X: This can be sacrificed to gain X mana this turn only
Quest: At the end of your turn, if the following requirements are met, do the following.
Behave: The following is in effect untill this attacks. Afterwards it is lost.
Level: Do the following whenever you play a card.
Drain: steal the following abilities from the target.
Invoke: Gain a 0 mana copy of targets deathrattle and battlecry.
Ally X: Do the following if X friendly minions with the same tribe as this are in play. This must have a tribe for it to work.
Critical: When this attacks a minion and it survives, do the following.
Vainglorious X: After killing a minion, if owner has X mana, spend X mana and do the following.
Ranged: This is immune while attacking.
Enlighten X: At the start of your turn, gain X temporary mana.
Overgrow X: At the end of your turn, if you have at least X unspent mana, do the following.
Stun: Stunned minions cannot attack until the end of their turn.
Disabled: A disabled minion is efectively silenced and cannot attack.
Spoil X: Like a druid "choose one" ability, but gives option of paying X mana repeatedly to gain the following effect or to stop doing so while there is enough mana.
Bodyguard: This is guarding a target and takes damage in place of the target.
Cleave: When this attacks, deal its damage to adjacent targets.
Piercing: Damage dealt by this in excess is dealt to the enemy hero instead.
Glory: Do the following if this kills another minion and survives.
Barbed X: Whenever this is attacked, deal X damage to the attacker before the attack.
Wander: When this is played, it is only summoned into play at the start of your turn.
Ritual X: The following effect remains in play for the next X turns.
Madness: 50% chance to attack a completely random target.
Benevolance: This can choose to "attack" friendly minions to heal them instead.
Trample: If this kills something as a part of it's attack, it can attack again.
Oblivion X: Do the following if X minions have died this game.

Please don't be upset if it doesn't quite look like the original, as I tried to represent them as the core of what these abilities meant. For instance, spoil can be either a battlecry or a start of turn effect. Only real problem was with sacrifice X and similar abilities as the game currently doesn't have any method of "activating" abilities that are on minions, unlike other ccg's.

Sunder: destroy target minion; its controller summons 1/1s equal to its power

Next keyword: Might

Might: This minion gains +2 attack every time it attacks

Example:

Master Armorer: 3 mana 2/4, Might, Deathrattle: Gain armor equal to Master Armorer's attack

Next Keyword: Shift