It makes sense why MissingNo accompanies Ash. Naming Red "Ash" in the Gen I games makes MissingNo appear via the Old Man Glitch. While normally MissingNo only appears at Cinnabar Island, Ash has already been there in the old timeline.
Delia and Yellow being a Composite Character doesn't make sense at first glance since their Bloodlines in Reset are different (Delia is a Lucario Bloodliner, Yellow a Heal Pulse Bloodliner). However, one should take into account that Lucario can learn Heal Pulse; the only problem with that is that Riolu cannot, so you have to evolve Riolu fairly quickly.
