Earth Spike: A large golem fist bursts up out of the ground, pounding enemies high into the air. The fist crumbles into a proper spike, as the enemies fall to do additional skewering damage. Optionally, the fist pounds the ground to do damage and knockback to things nearby before crumbling.
Chain Lightning: A bolt of lightning crackles down to strike the player when the spell is cast, creating a electric bubble field around them without damaging them. Chain lightning can now bounce off of the player, if there are no other enemies nearby to bounce it off of and the player is near enough to the target enemy. Optionally, when the lightning bolt strikes the player, it causes bolts to fire off at every nearby enemy which can in turn bounce between all other enemies.
Wind Slash: I'm gonna admit, I haven't seen anyone who even remotely enjoys or uses this skill. It's slow, it's easy, it's hard to aim, it requires you stand still and be vulnerable. It's all risk with very little reward. It's difficult to learn, difficult to master and once you master it... you would still be better off with any other magic skill, it seems like. The only way to redeem this skill would be to make it so that once you charge it up, you can't get your EP back from canceling it - but the arrows spinning around you can damage enemies who come into contact with them at a reduced amount of damage, causing that arrow to pop. At least then I could have some sort of protection while I waited for my arrows to get in a good position.

That said...
Wind Slash's final could be akin to the Season Autumn Mage's special skill, causing the arrows to launch out hurricanes that suck up enemies they rip through, damage them so long as they're in the hurricane and launch them far away.
That, or it causes the wind slashes to ricochet off of enemies and obstacles to bounce around.
Insect Swarm: Become the Lord of the Flies. You can carry one fully charge swarm of insects with you that take a long time to die, only truly starting to die off once they descend on an enemy. Optionally, you summon a Plague Mother Insect that flies over to attack an enemy. When she bursts a massive swarm of insects descend on the enemy.
Frosty Friend: Frosty Friend gains the size of and attacks of a yeti. It can slow enemies with icy breath, pound the ground to knock them awake or just punch them like usual. Optionally, it just gets massive and attacks normally like usual, but becomes like a Russian Nesting Doll. If the giant snowman dies, it melts into a tier 2 snowman. If the tier 2 snowman dies, it melts into a tier 1 snowman. Tier 1 snowman, after a short while of being at full HP, can regrow automatially into tier 2. And in the same way, tier 2 back into tier 3.
Ice Nova: A small, localized blizzard forms around the player for several seconds, damaging and slowing any enemy that comes into the blizzard. Potentially freezes them solid.
Ice Spikes: Causes a chain reaction of increasingly larger spikes to burst out away from the player, farther an farther, then shatters into a flurry of snowflakes all at once that slow all nearby enemies.
Smash: Creates a sound like the smash attack from Smash Bross and a tiny explosion from the impact, sending the enemy - regardless of it's size, flying around the area like a pinball to bounce off of anything it takes up to # times or # feet, receiving damage from every ricochet.
Heroic Strike: Adds a third hit to the end of the strike, ripping open and resealing a chasm in the ground that travels in a cone shape away from the player, hitting the target enemy and enemies within the cone shape. Optionally just creates tons of cracks in the ground with fire/lava bursting up from them for the third strike, that quickly vanish.
Dodging Strike: The player vanishes outright for a full second, then rapidly appears and disappears all around the enemy with a series of lightning fast slashes, dealing # damage total, finishing with a dash through the enemy on the other side - a flutter of feathers or cherryblossom petals left in their wake. It is a 'stylish' skill, after all.
Spirit Slash: The spirit gains a finishing move chosen at random from one of the other 1-handed skills. It can dash through an enemy, blade flurry them or leap back, forward and slice into them. Also, maximum charged Spirit Slashes will wait # seconds for an enemy to come into range before looking around, shrugging and vanishing. If an enemy does come into range, it will immediately trigger as normal. Optionally, for it's finishing move it surrounds one / all enemies in range with 4 spirits that slash at once for large damage?
Berserker Style: A fiery red aura pulses from around the player, increasing with their combo. At large combos enemies create small explosions on death, maybe just for visual style or actually causing additional damage to nearby enemies.
Shadow Clone: Adds one last, incredibly slow clone that deals massive damage with each slow swing. If you can keep an enemy contained to one spot long enough for the slow clone to reach and swing at it, it's worthwhile. Maybe the final shadowclone could have a unique shape - the shadow of your father or mother, maybe?
Haste: An hourglass forms over each player's head, then shatters and scatters hourglass sand immediately nearby players. On top of speed being increased, nearby enemies all have their ATKSPD decreased. Optionally, increases all player's movement speed until a hit is taken.
Protect: Causes divine light and Gridnea Goddess feathers to flutter down around players, leaving behind one feather that floats around each player. This feather dramatically reduces damage taken, but vanishes after # hits, leaving only the base Protect spell.