Where should I train?

First question, has the place Gilglum appear in Ailily? If so that is a very good place to practice. Tip: Make sure you have a party before fighting Widershin. It will be very dificult if you don't. And also make sure that you're members are lvl 55 or above. Its very dificult to fight Widershin, I remember that I was lvl 60 and my party was around lvl 57 when I defeated Widershin. Hint: Have a priest in you're party, 2 close combat fighter and always bring many gels with you. Help the priest in healing your party once in a while. Also bring life bottles.
GOOD LUCK!!!!!

There are a few Strategies for beating Widdershin. Here are a few "Do's" and "Don'ts" for fighting Widdershin:

DON'T Down Widdershin if you can Help it. He'll just Teleport to another area which makes beating him a lot harder.

DO pound him with everything you've learned through Leveling up. Trust me He ain't easy! You're going to need it!

DO Bring a priest/Healer with you in your Party. You'll Survive way more than if you didn't!

DO bring every Healing Item you can obtain! Sometimes the priests can't keep up with healing your party. Assist them in their job by restoring their Health, Magic Energy, etc.

DO learn your "Mystic Artes!" learning your finisher move makes beating him A LOT easier than if you didn't know it!(Here's how: Use every Tech/Arte your job knows 50 times in Overlimit State in order to learn your Mystic Arte, In battle, when overlimit is active,press L+R, Pound your opponent with an arcane type move+hold the "X" Button)

DON'T randomly pick teammates! Just because some of your teammates helped you out in other quests, doesn't mean they'll be good when fighting the final Boss, so be selective!

DO Train, Train, Train! Practice against powerful opponents, learn their moves, know how to react to them, and know when to attack, and when to guard.(a great sparring partner would be the "Gold Knight" whom can be found in Magic Map Dungeons)This will help in getting you and your teammates stronger!

DO have a Trump Card Handy! Bring a Teammate(It can even be you) whose finisher move attacks a WIDE Area, then you don't have to worry about Widdershin Avoiding one of your Strongest moves!

DO wear the appropriate equipment! Make Sure you're wearing Powerful Equipment and the appropriate Good luck Charm(Note: Wear the "Light Cape" so you only take half the damage from his Giant Sword)

DO use Items! At the Start of Battle use the Magic Lens on Widdershin, so you know when he's Near Death So to speak^_^(Widdershin's info will then automatically be added to your enemy book)

DON'T stop moving! Just Standing around and doing nothing spells DEATH! Not only for you, but you're entire Party as Well!

DO have the Appropriate Title! Make sure your Character's Title is a helpful one, because once the battle starts, you can't change your Title until the battle is over!(the best one would have to be "Paladin"-Immune to Staggering)

DO Protect your Teammates! If one of your Team members is getting pounded, try steering Widdershin's attention on someone other than your teammates.

DO use "Unison Attacks!" some artes won't be enough to thoroughly pound Widdershin. Try using unison attacks to take him down faster!

DO adjust your Strategy! Some Strategies work better than others. Try different Strategies and see which one works best for you.(EX: Hold your Ground, Guard, Charge, etc. Can be found in the "Strategy Menu")

DO switch between party members! If the Character you control gets KO'd then change to a different party member immediately by setting the Character you want to use in "Semi-Auto Mode" by selecting the "Artes" Icon on the Battle Menu, and pressing "START" until you find the one you want to play as!

DO Infect Widdershin! Use moves like: "Acid Rain" to lower Widdeshin's Defense, Try Stunning him with "Pow Pow Hammer" for Example, or even try Sealing his Magic with "Silence"(NOTE: this move Did NOT work on the Gold Knight, so don't be surprised if it Doesn't work on Widdershin)

Follow these Rules when battling Widdershin and the Battle Should Be a piece-o-cake

If you are lv60 you can just bring along a healer cos I did that and won

Well firstly, if you finished the game once, go to HARD setting, bring 4 people with you, then go to WEALD on HARD. Now, before you do this- make sure you have all potions maxed, make sure to bring at least 1 priest with you, as for your title, if you finished the game have the "town saviour" as your title, however, if you haven'y use the title depending on your radiant equipment.

Strategy for Widdershin is to keep pounding, keep getting unison attack or do a mystic arte, if you have learnt all, using all skills 50 times. Once in Overlimit gauge, press L+R, do an ARCANE-TYPE skill then hold X. Make sure to use Light cape to halve the damage from the blade. Good luck...