Agree as what other anons stated. But I would like to add that: You can farm skills from any LDs. GX world or DM world doesn't matter. I myself particularly likes to farm skills from event's LD, because you dont use your keys, and you can earn reward. 2 birds with 1 stone. Of course I mean if you have skilless farm deck.
For example: since Crowler event until now the Jesse event, I got Bastion's "spark" "plasma" "Gaia" as well as Alexis's "master of Rites".
Good luck
anoymous
Bastion only have to watch out his 2 magic cylinder, but you can also to farm skill from not GX characters, such as Yugi or Raptor that are easier.