heyo, welcome to torchmodders

just from reading, the problems you have could have come from copying a skill and not changing the GUID, or there could be just some weird setting in the missile file and unit spawner

if you dont mind, post your mod file so i can have a look and see whats wrong.

ok fixed it and made it arc properly
it was simple to fix the targeting, but arcing missiles are pretty technical, and i had to edit more than just the skill file
anyway, ill try and break it down so you can somewhat understand whats going on lol. 1st the skill code and the changes i made.

[SKILL]
<STRING>NAME:RangerFireArrow
<TRANSLATE>DISPLAYNAME:Fire Arrow
<TRANSLATE>DESCRIPTION:The Ranger Lights an Arrow and Launches it at Their Enemies.
<TRANSLATE>BASE_DESCRIPTION:Fire Arrow
<TRANSLATE>REQUIREMENT_DESCRIPTION:Requires a Bow or Crossbow to use.
<STRING>SKILL_ICON:skillicon_longrange
<STRING>SKILL_ICON_INACTIVE:skillicon_longrange_gray
<STRING>ACTIVATION_TYPE:NORMAL
<STRING>TARGET_ALIGNMENT:EVIL
<STRING>TARGET_TYPE:POSITION
<BOOL>USEWEAPONANIMATION:1
<FLOAT>RANDOMRANGE:0
<FLOAT>RANGE:15
<FLOAT>TARGETRANGE:3
<FLOAT>RANGEMIN:3
<FLOAT>MANACOST:4
<INTEGER>COOLDOWNMS:1000
<FLOAT>FINDTARGETANGLE:360
<FLOAT>TURNRATEOVERRIDE:-1
<BOOL>CAN_BE_SILENCED:0
<INTEGER>LEVEL_REQUIRED:0
<INTEGER64>UNIQUE_GUID:3240634451233832361
[REQUIREMENT_LEFT]
<STRING>UNITTYPE:BOW
<STRING>UNITTYPE:CROSSBOW
[/REQUIREMENT_LEFT]
[LEVEL1]
<FLOAT>RANDOMRANGE:0
[EVENT_TRIGGER]
<STRING>FILE:media/skills/ranger/fireearrowranger.layout
<FLOAT>CHARGESCALEPCT:10
<BOOL>CAN_CLONE:0
<BOOL>BUILD_CHARGE:1
[/EVENT_TRIGGER]
[EVENT_MISSILEDIE]
[EXECUTE_SKILL]
<STRING>SKILL:FIREAOERANGER
[/EXECUTE_SKILL]
[AFFIXES]
<INTEGER>AFFIXLEVEL:1
<FLOAT>DURATION:4
<STRING>AFFIX:ARBITER_MAGMA_SPEAR_IGNITE
[/AFFIXES]
[/EVENT_MISSILEDIE]
[/LEVEL1]
[/SKILL]

what i removed
   <FLOAT>SLOWDOWNMS:2000
   <BOOL>DONT_STOP_ON_DEATH:true
   <STRING>TRIGGER:HIT
   <BOOL>CAN_PROC_FROM_SKILL:0
these are just superfluous for the skill, they have other applications elsewhere but in this case they do nothing.

         <FLOAT>TARGET_AHEAD_OF_UNIT:2
         <FLOAT>LINE_EMITTER_OFFSET:0
         <STRING>FIREFROMBONE:RIGHTHAND
         <STRING>FIREATBONE:CENTER
more lines at the event strings i took out
fire from/at bones lines had to be taken out since they are the main culprits of the wonky targeting, they force the missile to always fire from the characters right hand bone and fire at the center of a targeted unit, if there is nothing targeted(aiming on ground) the missile will careen into a random direction

what i changed
    <FLOAT>FINDTARGETANGLE:360
for monsters its set differently so they aim at certain angles towards the player. this is also used in skills which require targets to give it an angle to where it will snap and acquire the target regardless of where the mouse is located, the radius is controlled by the max and min range

   <FLOAT>RANGEMIN:3
changed from 6 so the missile can arc at close range and still hit whatever is in front, if its set too high you wont be able to hit anything close

what i added
   <FLOAT>TARGETRANGE:3
this sets the minimum distance you can select targets, its different from range min since this range applies when you physically click on a target

now for the missile file, this is key to making the missile arc propperly
you only need to set some things to false in the side menu to get it working

TARGET POSITION: FALSE
this makes the missile free from targeting constrains and lets the skill handle the targeting, this is typically used for straight trajectories to control where the missile will end. this is a minor part of what made the targeting wonky, since the missile is asked to end at the target area, but is also given a set distance to travel, so it ends up exploding in mid air

COLIDES WITH OBJECTS: FALSE
this is to make the missile arc at close range properly, if this was set to true the missile will instantly collide with any unit in front and not perform its arc, this is typically set to true for straight trajectories and missiles which dont have a following missile die event

ARCH DISTANCE: 0
this will force the missile to always go a set distance when it arcs, if set to 0 the missile can arc freely though out its max range and enables it to be aimed at targets properly

now for the unit spawner settings within the layout file,
the only thing that had to be done was shift the Y axis of the spawner up to 1.5
since the missile no longer spawns from the right hand bone, we just have to set it to spawn a bit higher up so it aligns with the character and doesn't instantly collide with the ground.

thats it
this is what it looks like after the changes.
i want you to try and do this yourself so you get a better feel for GUTS and learn from it
gl and have fun modding.

Omg! 

Guys im tingling all over! 

Thank you immensely this is going to help massively!