I have created mucho spells for Final Battle (which I will list), but I have yet to work out how they would affect abilities. Here are some I've worked for that have special things that they do when Junctioned:

One: When One is Junctioned, the Junctioned attribute becomes the highest, but the amount it jumps up to become the highest is subtracted from the other attributes (so if you got 100 in one category and had 5 other attributes, each of the other attributes would lose 20). This can be used to bring up a dangerously low stat, or it can be used to make an average one really powerful (such as Magic Strength).

MindSwipe: The attributes reflect the mind-set of the character and of the enemy.

Death: When Junctioned to HP, prevents spells that hack down at HP (Quartr, Demi, etc.) When Junctioned to Magic Defense, defends against all death spells and reduces dark spell damage. When Junctioned to Attack, does damage based on enemy's HP as well.

Hyperdrive: The attribute is low the first turn, then becomes "hyperdrived" and slowly depletes again.

Chronos: Increases the frequency of bonuses to Junctioned attribute.

Creation: Favors the underdog attribute.

Finality: The attribute gets put further and further down per level, but when it is removed, grand gain takes place.

Null: Stops all growth in a particular attribute but gives bonuses in all others.

Entropy: Raises one other attribute randomly by the same amount.

Restorer: Raises one other related attribute.

Grand Life: Huge HP or Vitality totals. When equipped to Attack, randomly casts Life on undead enemies. When equipped to Defense, Regen and Life 3 gets turned on.