One of the issues I have with Mini Six and the D6 System is how the dice seem to really hurt supernatural powers. For instance, a Lightning Bolt has a TN of 23 and even at 6 dice I think I only once or twice saw a player being able to conjure up a bolt. My fighters and archers could usually hit a target, not so much the spellcaster.
So! I shall add a few house rules to help out. One is Mana Points, a concept that I generally like, and the other is building up magic.
Mana of course is the unseen energy that magic-users manipulate by the force of their will. As an energy, it is raw magic, it requires the will in order to change it to the desires of the caster, such as turning it into projected electricity or using it to rebuild flesh (Healing). The reservoir of mana that a character can take in depends on their mental capacity.
Each full die of Smarts adds +3 mana to a character's mana pull. Thus a character with 4D Smarts will have 12 points. At the GM's discretion pips can add +1 to a mana pull. Spells generally cost 1 mana point to activate and said mana generally recharges at a rate of 1 per hour.
Rather than a straight loss of power when a character fails to make a roll, this house rule allows the character to build up power instead. The character notes how far they have rolled and on their next roll if they wish to continue building up energy their roll will be applied to that number. Damage taken during the round, such as from an enemy attack, causes the spell to fizzle. Each use requires a point of mana to continue.
Example: Chadwick the Mage has 6D in Magic (4D Smarts, 2D Magic). He thus has 12 mana points and during the course of the magical duel with an Orcish shaman tries to summon a bolt of lightning to attack. He spends 1 mana point and rolls a 19. The TN is 23 and 4 is all that Chadwick needs to cast is another 4 points. If he wishes to continue next round he needs to spend another mana point (the Lightning Bolt is now costing 2 points instead of 1) and pray that the Shaman doesn't tap in quicker than he does and launch a bolt that interrupts his powering up. The next round he gets 18 which is added to 19 for 37. A success! The lightning bolt is now conjured and in his hand, as per rules, he must make a Throwing roll which is penalized unless he holds it until next round.