As they are all students to him, he will have dialogues with all the GX characters. Besides, each GX character has a special dialogue when facing other GX characters.
Yes. Each GX character had unique conversations with each other since they all live in Duel Academia. I'm surprised even Aster and Bastion had a special conversation.
Crowler and Boneparte naturally fears Aster because he is a highly-paid Pro-duelist, and Aster once made a remark to them, in order to utilize his duels for gains, they need to be his sponsors and with their paygrade, Aster doesn't think it even matters.
Tough choice, Konami didn't even want to pit Aster vs Yugi or Kaiba, so we can only follow what Pegasus' personal ranking choice at the moment: 1) Yugi 2) Kaiba 3) Joey 4) Aster 5) Jesse...So in a way, I would like to see Aster battle the top 3 in Pegasus' list.
Yes Aster have defeated both Zane and Jaden(but that only maked them stronger) and WAS number 1 "in the world" but for SOME NICK OF TIME in the series. In season 3 and 4 there are way better duelist than him. Like Jaden(Yubel), Dark Zane, Adrian Gecko and even Chazz defeated him(i dont even know HOW) !!!
And yeah neither of them have any chance against Yugi or Kaiba. OK maybe Jaden(Yubel)or Zane can put up a some good fight against Kaiba, but never against Yugi/Yami cuz Kazuki or the producers will NEVER let Yugi lose !!!