I've had several of these ideas.
Lucky Seven: This is a skill for a fan-made class of mine, the Gunslinger (and its promotion Sharpshooter). As the name implies, this class wields handguns, which along with hand cannons form the "Missile Trilogy" by which guns beat bows, bows beat hand cannons (weilded by Cannoneers and their promotion Cannon Troopers), and hand cannons beat guns. Back to the skill, it has a Luck% chance of activating, overriding Hit, Avoid, and Critical for both player and enemy, and resulting in two to seven (randomly selected) shots at half power to the enemy with a guaranteed hit rate. Lucky Seven only activates if a handgun is equipped. Statwise, Gunslingers and Sharpshooters are similar to ranged Myrmidons/Swordmasters, so this is basically their equivalent of Astra, learned by Sharpshooters ar level 5.
Flame Booster: Gives the users's handgun attacks a fire/anima attribute on the Trinity of Magic. Attacks are still considered physical handgun-based in all other aspects, and are still counted on the Missle Trilogy as well. This is learned by Gunslingers at level 15.
Advantage: Cannoneer skill, learned at level 15. Luck% chance of "mimicking" the enemy's disadvantageous weapon on the Weapon Triangle or Trinity of magic, granting all associated bonuses. This skill does not activate against bows or handguns, and will only activate if a handgun or hand cannon is equipped.
Trap Mastery: This is a skill for Rogues, learned at level 1 in games where all Thieves and their promotions gain Locktouch, so to give them something that Assassin's don't get. This allows Rogues to set traps, purchased from certain shops, on any adjacent, passable tile. When a trap is placed, an icon will appear over the tile, though this can only be seen by the army whose rogue has placed that particular trap (in other words, enemy units can't see them). The trap is activated when any unit, friend or foe passes or stops on the tile. Depending on the trap's effect, the unit may or may not be able to finish their turn. As most traps are activated by stepping on them, flying units generally don't activate them, but there are exceptions. When a Rogue sets a trap, they are granted some EXP. Used wisely, enemy units can be 'lured' onto spaces with traps. A few examples of traps are as follows.
Landmine - Creates a small explosion when activated, damaging the unit. The unit is still able to continue moving, and can finish his/her turn if the damage isn't lethal.
Tripwire - Halts the trapped unit's movement, ending their turn when the trap is activated.
Pitfall - Damages the unit and instantly ends their turn. This trap is rarer and more expensive than the Landmine and Tripwire traps.
Arrow Trap - Activated by movement rather than touch, this trap sends and arrow flying at the unit for some damage. This trap can be activated by flying units.
Poison Snare - Ends the unit's turn and inflicts poison status.
Disable Trap: Learned by Rogues at level 5, and perhaps other classes as well, this automatically activates when the unit steps on a trap. Rather than suffering its effects, the trap is detected and destroyed before it activates.