1) MTG has splitmana which allows 1 of 2 different colors to play it. ETG does not allow for such a thing, and i thought this might be a way to simulated that effect.
Simulating split mana in ETG would be more easily/thematically well done with Duality Quanta/Hybrid Quanta, which just directly aligns the card to two elements instead of banning a specific element and leaving the rest open to using it. Codewise, the method seems the same, but why would I favor 'banned elements' instead of 'card aligned with several elements'? (Alara's Shards and Ravnica's Guilds focused much more on how their colors tie together instead of how they lacked 2/3 colors, IMHO.)
2) fire is more aggressive, and this card is more a problem mechanically for fire than air. a card calld Tactics with antiEntropy would probably be my next creation is this idea could be refined to the point of workability.
I agree mechanically that fire is more aggressive, but I don't see your point thematically; while Fire may be the element that is most ready to fight, Air is the element that directly opposes Earth. In addition, Air's defense is about Evasion and dodging as opposed to Earth's 'prepare to get hit' mentality, so I would think Air favors an 'Evasive Stance' much more than a 'defensive stance'.
However lets talk about Shield. Shield is a generic DR shield that originally belonged in Death, Life and Light. Many have noted that its effect does not seem to fit Fire. How could we mechanically represent this in as simple a manner? Russianspy's suggestion would require adding 12 quanta types which is medium effort for this desired effect. Can we identify a simpler method?
I think if you really want to alter Other cards to avoid thematic conflict, it would be best to have -some- cards that do not fit in an element have a 'modal' alternative when you're wielding that element (sort of like the mark bonuses on some of the Other-type weapons.)
Using the shield example :
1) Fire is an aggressive element - it doesn't like to play defensive and prefers damage + CC + Quanta Acceleration.
2) DR is not fitting for Fire because Fire cards have low HP, no way to raise HP, and use other methods for defense (Usually ones that maintain tempo, threats, or pressure such as Phoenix, Seraph, and Fire Shield respectively).
3) Fire likes to deal damage in exchange for damage. (Fire Shield, Rage Potion)
Therefore, Shield could have something like :
Shield
1 :Other
Shield : Reduces 1 physical damage per attack.
Shield Bash : If you possess
quanta, Shield deals 2 damage to a player the first time you are damaged instead.
Alternatively, an antiElement card could instead have drawback that triggers when you use it while having the 'wrong' type of quanta. (E.g. Defensive Stance gives the target -1/+1 when you have Air quanta.)
At the same time, however, Other-type objects can be '
generic' weapons and equipment created for use by
everyone - a Fire Elemental may not benefit the best by using a Shield thematically, which is reflected in Fire deckbuilding rather than having specific cost bans on the card (Firestall usually favors the damage based Fire Shield coupled with healing), but it is still usable by it if he really wants to build a defensive style fire deck. IMHO giving specific interactions/restrictions (effect-wise > cost-wise IMHO) is possible, but it seems a bit nitpicky when one considers that such a card might not be ideal in the Elemental's playing style to begin with. (A trained Graviton Soldier will obviously value a shield much more than a Fire Beserker but both have the option to equip it because its designed for anyone. A similar parallel would be an RPG where a class specializes in a certain weapon but can wield others with a skill penalty as opposed to a complete 'class ban'.)