Psychic Spark creates one additional dart whenever Magic Missile is cast.
The Shield spell causes the caster to take no damage from Magic Missile.
The level 10 wizard's Evocation School class feature Empowered Evocation will add the wizard's intelligence to each missile.
When interacting with effects like Death Ward and dealing multiple attacks to the same creature, assuming the 1st attack was sufficient to down the target the 2nd attack appears to apply before the Death Ward activates, which means that after 2 attacks the target would lose the Death Ward but remain with 1HP. If the initial attack would have 3 applications then the target would be downed on 1st attack and again on 3rd attack. In case of Avatars it means that, whilst having a Death Ward applied, they would need to receive 6 attack applications to fully die: 2 to break down the ward, 1 to get downed and 3 more to fail 3 Death Saves. This effect seems to apply to all multi-application attacks, like Scorching Ray and Eldritch Blast (as of 4.1.1.3669438).