* Recruits jack later on with ur charcter all in a higher level. He will
  come in with a higher level and u could concentrate training the main 
  4-5 characters. With him,u can open locked chest.But to be honest items
  in locked are useless. Get him only when in are near the last few level,
  only items behind in chest are useful.
* My advice is dont ever take gavin into ur party. Take Nico first...he 
  can use a sleeping spell. When u gets the north wind,takes gavin and get
  nico out for final battle...gavin will join with the same level around ur
  other characters when u recruit him.(provides that u don't recruit him 
  once before.
* Be sure to married off character before finish battle for different ending.