Permanent Spells
Most spells, when played, do an action and then promptly disappear. For example, Blessing of Kings gives a minion +5/+5, and then it's done. There's no continued effect. So forget that, because for this theme you'll be doing the exact opposite.
Your card must be a class spell that has a permanent and reoccurring effect on the game.
Make sure your card has some way to interact with it being played multiple times. Do the effects stack? Or does something special happen when played again (Like with Shadowform)?
The best examples for wording are tied with minions like Naga Sea Witch and Cult Master as they give a passive effect until removed. As a spell, this removal will never happen, so remember to balance accordingly.
Currently, Shadowform is the only example in Hearthstone, but The Mistcaller also gives a very good example with it's Battlecry. Regardless, I've included a very basic example of what your card might look like.
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Chen Stormstout is Lili's uncle!
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Mermaid
"With my lovely voice, I take all the men on my path to meet the fury of the seas."
First of all, I mean I do not speak very good English, but I'll try.
Hero: Serena Morin
The Mermaid Class is only focused on maritime and related topics. There is no letter for this class without any relation to the place where Serena Morin came. As everything is based on water, the Heroic Power of Serena Morin is a swirl. The Swirl simply reverses the attack and health of a minion, opening multiple paths to thunderous plays.
As the mermaid song is something that delights, that will be used to create new strategies for the game. This new class brings a new mechanic: Charm.
The Charm will give a unique effect to a minion, and this effect can only be performed once after follow the directions written on the card.
A good example of this mechanic in a Basic Card:
With Battlecry or Deathrattle this card would be too overpowered. But the Charm limits you to activate its effect if the Ancestral whale survive for 2 enemy turns. This leaves more difficult and you have to develop strategies to protect the card so that the effect is activated.
Another example in an epic card:
Note that the effect of this card can only be activated the turn it was played, differentiating the Deathrattle. You have to be able to kill this lackey somehow in the same turn to get activate its powerful effect.
We can not forget a spell using the same mechanics:
Only a minion can enable Charm, is written as in the examples: Die at the turn it was played, When you attack, Survive 2 enemy turns, is referring to the minion, not the hero.
Of course, don't there will be only animals cards, also have cards of marine plants, differents mermaids, fantasy characters and places like Atlantis, or perhaps even surfers, haha. :P
Serena Morin can be pretty aggro and control, exchanging the Attacks and Health minions to hit the enemy hero or take control of the battlefield. There is plenty of decks to Mermaid using neutral or class cards and that makes it a powerful class. Think of the endless possibilities using Swirl and Charm!
I hope you're all right! Sorry if I missed a word, for I speak Portuguese. Thank you!
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a Druid murloc card
Next: A 2-Cost 2/3 class card.
2
A powerful Jomungar
Next: a 7+ cost minion.
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A beast with inspire that gives some sort of a new spell or something.
Next: 2 Tribes minion (Murloc + Pirate, Demon + Mech, ...)
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A Murloc for Rouge with Stealth.
Next: A Secret that summons an existing collectible Minion.
Done:
Next: A secret for a class without secrets.
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A Rogue spell card.
Next: A spell to summon minions
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For Questing Adventurer
Next: Floating Watcher