I had a bit of time today and I thought I'd sketch out an idea of what a stealth based mage might be like. Now, as I understand it stealth is one of the most difficult things to introduce to a game because it can become overpowered very quickly if not handled right, and this has been brought up on the forum before. With this in mind I came up with a Ninja hero below as a rough outline of how I think this sort of mage could be done. I also personally think it would be really cool and fit an interesting style of play.

Ninja: Health, channeling and so forth are details best up for balancing and not my main concern.
Training: War and Air (I originally thought War and mind, but I think air is a better fit for some of the potential cards)
Triple Cost: Arcane, and Soldier creature cards. (Bear with me, I'll explain this below).

Thematic Play Style: The Ninja has access to war spells especially of the command incantation variety, but he needs to be differentiated from the Warlord mages by making him less creature focused. The goal is to make the mage himself a flexible solo player, or good at commanding small groups of unique creatures. Think of his go-to creatures as similar to Sir Corazin, Blademaster of which he controls between 0 and about three to fight. The Ninja could be encouraged to do this by having a few unique ninja creatures with special combat roles to fill. In order for this, the Ninja can't be encouraged to play the same creatures as the Warlord, but as it is almost all War creatures have the soldier subtype (excepting Guard Dog which maybe a Ninja would use?). So, the way these creatures become useful without being overpowered is by making them cheaper to the Ninja by being non-soldier war creatures, and by making his abilities work well to increase their flexibility (the main theme).

Abilities:
1. Passive Obscured Trait. Assuming this isn't too powerful, this forces certain opponents to play very differently against the Ninja because of his ability to recover at range and avoid range attacks such as from the Wizard's Tower.
2. Command incantation spells are returned to the spellbook after being resolved. Now, this is the heart of what will make the Ninja flexible in combat. Without the commitment of enchantments the Ninja can be much more surprising by pulling out piercing strikes, power strikes, evades, flank attacks, whirling strikes and so forth. The distinct advantage of doing this will allow him to carry one of each, though perhaps two of important commands in cases of nullify. Because of this he will be comfortable not running duplicates and putting more situational command cards into his spellbook. If the current commands are deemed too strong, because this certainly is a powerful ability, a new subtype could be created (i.e. maneuvers) that do similar effects but resist crossing themes with spells like Akiro's Battle Cry. Although, I think if commands were used then the Ninja's integration into the existing card pool would be a lot smoother and allow more options immediately. This is what I imagine would require an astronomical amount of testing to discern if it could be balanced.

New Condition: Concealed: When a creature is concealed it cannot be targeted. The concealed condition lasts for Dissipate X. So this will be the main stealth mechanic used. Making something unable to be targeted has obvious potential problems, but I think it can be balanced if implemented like some of the cards are below. This is also the first condition with a dissipate trait, so some people might find issue with that.

Some Example Cards: I leave level, mana cost, etc. up for debate because that requires a lot more balancing then I have time to theorize about.

Equipment:

Kunai Set: (Weapon or Belt? War, Ninja-Only) Small melee quick attack, unavoidable. 5 tokens. Ranged quick attack option, remove 1 token after each use.

Dark Cowl: (Head, Air) When not in LOS of an enemy creature, this mage can pay 2 mana for the concealed condition dissipate 2.

Black Robes: (Torso + Pants, Air) Gain Elusive, 6+ d12 x3 melee defense. Give -1 to d12 die rolls after each time the defense is used that turn. (6+, 7+, 8+ effectively).

Ring of Precision: (Ring, Air) Convert up to 2 damage to critical damage once when this mage makes a melee attack this round.

Katana: (Weapon, War) Piercing, Sweeping or Doublestrike options. Aside: Not sure with this one, but I'd love it if MWs introduced a sheathing mechanic where one weapon could be disabled (intentionally) and another weapon used in the same slot, being able to switch between the weapons. This would make certain weapon cards more viable I think.

Blowpipe: (Weapon and Shield, War, Ninja-Only) Weapon can either poison (perhaps Weak) or put to sleep at range.

Incantations: Remember these commands could be maneuvers instead

Backstab: (Command, War) All damage from the next melee attack this round is critical. This would be like a more expensive Piercing Strike.

Assassinate: (Command, War, Ninja-Only) Kill target Non-mage corporeal creature if attack is not cancelled. (Expensive, perhaps only able to be cast on Ninja subtype creatures of high level)

Weave: (Command, Air) Gain Elusive and Fast this round.

Escort: (Command, War) Target creature gains Guard and Intercept until the end of this round.

Swift Strike: (Command, Air or War?) This creature may attack at the beginning of its activation this round leaving a quick action remaining.

Shadow Step: (Command, Air, Ninja-Only) Like a slightly cheaper force push but for friendly ninja creatures only.

Ambush: (Command, War) All attacks against target creature gain unavoidable and +2 melee and +2 Ranged if completed by a concealed creature.

Smoke Bomb: (Air, Ninja-Only) Everything in target zone gains the concealed trait dissipate 1 and LOS between all characters in zone is blocked. This would include both friendly and non-friendly creatures.

Enchantments:

Mark Target: (?) Target cannot be concealed. Dissipate 2.

Dart Trap: (War) Some sort of face down zone enchantment dealing that can be activated upon command and deals damage. I haven't thought much more about this one.

Conjurations:

Wall of Smoke: (Air, No visibility) 6 health, 0 Armour. Not able to be targeted. Dissipate 3. I like the idea of the Ninja using the fog bank a lot more to make full use of his dark cowl which would be the main way of gaining conceal. The wall of smoke would do a similar thing but because it can't be targeted it would be a more reliable use of quickly concealing though it wouldn't remain on the battlefield.

I haven't thought about creatures or any other sorts of conjurations. This was really something I just thought up on a break while working on a term paper.

Synergies: Alright, so the reason I think this sort of a Ninja could work without risk of being abusable is because his passive isn't overly powerful (though some may contest this) but it preserves his stealthy theme. However, concealing himself isn't easy requiring a constant need to break LOS and use the dark cowl for a dissipating effect. The only other method would be to cast a smoke bomb for a turn of conceal for the mages creatures and the breaking of LOS in order activate the cowl. To use this in concert with Ambush if the opponent mage is in the same zone would be a need to cast Mark Target on him. Perhaps all of these steps will give him a chance to respond.

Other Thoughts: The reason I went with air instead of mind was to encourage the Ninja mage to play differently then the Forcemaster when it comes to defense and mobility. With the Ninja's flexibility, likely frequent use of cheap LOS blocking walls and cards like Shadow Step which gets returned after use, he is mobile enough to not bother with teleport in many cases. I personally love the little effect cards like Brace, Defend, Knockdown, Stumble, Fumble, Decoy, etc. I like to anticipate the opponent and cast that little cheap spell that just throws off his combat strategies and reply with my own well timed plays which is why I thought the Ninja character would be a fun way to do this as a main strategy.

Let me know what you think of the idea, what you think is good or bad or needs a lot more thought. This was a pretty quick thing for me, so I know that it won't be perfectly balanced, but initial ideas rarely are. It's whether the core concepts are salvageable and can be implemented and if its of interest. I honestly don't get to play Mage Wars near as much as I'd like, so I wouldn't say I'm too practically experienced with the game. If you have additions or other thoughts let me know too. I'd love to flesh this out, as I'm big on testing new ideas and making personal variants for the occasional unique experience.

I also haven't seen the interview, but I think most of the perceived problems aren't only avoidable by restricting what the siren can do. I think a more flexible way of approaching the perceived issues is by considering what she wants to do. What I mean by this, suppose the siren has her own unique spells that fill in a niche similar enough to hellfire trap yet more in line with her own range of intended thematic play styles. If a siren mage player really decides that hellfire trap would work better they can do that fairly easily, but the player may be incentivized to play another way.

This doesn't only need to be accomplished by making similar cards, but by making a play style different enough that the cards which seem more thematically unique are generally preferable for use in tandem with powerful class only cards and the mage ability. We can already see this with the Warlock and Necromancer. The few cards that the necromancer have that synergize with zombies or skeletons make it so that he would choose to use them even if the Warlock would not despite their similarly low spell point cost.

I haven't actually taken a look at anything regarding the new classes, but given the success in this regard in the past, I'm not too concerned. My overall point is, theme shouldn't necessarily limit what a mage can do, just direct a unique way of playing that compliments the theme. I hope that helps ease some concern.