Whether or not Da Undatakah can pull himself from your deck depends on the order the deathrattles execute. If Immortal Prelate's deathrattle fires first then Da Undatakah will be in your deck when Silver Vanguard's deathrattle executes and can pull himself. If Silver Vanguard's deathrattle fires first then Undatakah won't be in your deck yet and can not pull himself.
Undatakah's deathrattles will always fire in the order that he gained them. This order matches the order of the big cards you see when his battlecry fires. Undatakah gains deathrattles in a random order, which does not correspond to the order the other deathrattle cards were played or died in.
Josh Durica
Whether or not Da Undatakah can pull himself from your deck depends on the order the deathrattles execute. If Immortal Prelate's deathrattle fires first then Da Undatakah will be in your deck when Silver Vanguard's deathrattle executes and can pull himself. If Silver Vanguard's deathrattle fires first then Undatakah won't be in your deck yet and can not pull himself.
Undatakah's deathrattles will always fire in the order that he gained them. This order matches the order of the big cards you see when his battlecry fires. Undatakah gains deathrattles in a random order, which does not correspond to the order the other deathrattle cards were played or died in.