Headscratchers / Jujutsu Kaisen

• Why didn't Nanami finish Mahito off when he had the chance when he was crushed under rubble?
  • He was out of energy. If he dug him up, and it turned out Mahito could recover from his injuries (which proved to be the case) Nanami would be at serious risk of getting sucker-punched.
• Why doesn't Mahito just make a million of himself to gang up on Yuji?
  • It wouldn't be very effective at all. In the Shibuya Incident arc Mahito makes a single clone of himself, however, said clone is not able to use his innate technique, idle transfiguration on others only himself. So the clone loses arguably one of his strongest abilities as idle transfiguration only requires him to touch another person for him to warp their body into a horrific monster. So at only two Mahitos, the second has less abilities. It's safe to assume that more clones would be weaker with less and less strength and ability the more clones there are. So a million clones would likely be very weak and Yuji would be able to easily defeat them.
  • To add to this Mahito divides power between his clones, aka conservation of ninjutsu