The one responsible for his mother's death as far as Yulian's concerned at the moment is Venersis. Even if he didn't cut her down himself, he was the commander of the attack that she died in. This was on the orders of the now dead father of the current Glow, who claimed to have not been in his right mind back then. If Basura is at all related to that situation, it hasn't really been mentioned yet. He might not have even been involved in that attack, for all anyone at this point should know anyway. If he was there, his repeated escapes could be build up to that reveal, or it's just happening to draw out the confrontation between Yulian and the man he fought with and who made him realized there's a lot more people around who can fight at around the same level he's on right now.