ways of micro-influencing card power toward balance

[aefields]

Often, the obvious way to downgrade an overpowered card results in an underpowered card.  How can overpowered cards be balanced?  The same is true for underpowered cards.

For cards of limited duration, doing slight damage to the owner can be a way of fine adjustment.  A small chance of a card not working is another (only for chaos, of course).  Reducing effect vs. one or more elements can turn a 'must have' card into a 'very good but not perfect' card.

For example: I think that Phase shield is overpowered.  But reducing it to two turns from three would be too much.  So: some possible minor depowerings: do one damage to the owner every turn it is in play.  Or a geometric increase in damage - whether based on individual shields or based on all turns when a shield was active over the course of the game. Limit the number in a deck (five instead of the usual six).

Damaging self, limiting number of cards below standard... what are some other good ways to limit cards that are good for the game but slightly overpowered?  The best way of limiting will be different for different card effects.

Personally, I think that it's ok to have underpowered cards in a game - they just don't get used... unless someone is tricky with them.  But to bring them up to their potential, reverse options apply: small health bonus or suchlike.

[OldTrees]

Valuable but could be expanded.

[Keeps]

I would also note, that over powered cards only appear over powered relative to the cards facing it.
Using your example, the phase shield is a joke, even a liability against gravity, fire and darkness, but it's a show stopper to life for example.   Until this game has every element having at least one way to neutralize a basic concept, and also rainbow to be adjusted a bit to not be so immediately expansive.  Then cards will always seem over powered.  Giving life at least one form of PC even though it maybe very weak form of it, would go a long way.
Time and Aether could all use something similiar, like a rewind for a perm, and a phase out for a perm...  A lot of creative things could be done, like life could have a card called overgrowth, the player has until the end of their next turn to repay the quanta cost (cleaning costs) or the perm is overgrown.  The perm then can't be used or destroyed until the overgrowth is destroyed, an attempt to destroy, destroys the overgrowth  Make it cost 4 life quanta.  It could be a way of disabling a perm, forcing a player to pay more quanta, or a way of protecting a perm you cast early, but want to actually use later.  While at the same time being expensive to cast compared to the other elements.  Regardless no card will be so greatly OP that it shuts down certain types of battles, like mono-aether does.