I'm thinking of a Magic Missile variant. It uses the fire element (instead of Force) and requires to touch attack roll to hit. Shield still defends against it, as does elemental resistance.
The missile scales up to level 9, just like the cannon Magic Missile.
It requires a touch attack, thus a save is not allowed.
It is still a 1st level spell.
Range and other characteristics of the spell are the same as Magic Missile.
Lastly, the spell persists for one round per caster level until a successful attack is made (vs Magic Missile which automatically hits on the first round). While the spell is "held" other casting is not possible, however the spell can be cancelled as a free action at any time.
Alternative: for this might allow for different elemental types such as Freezing Missile or Static Missile, etc. if such a choice is made at the time the spell is prepared.
Alternative 2: might require "meta-magic: energy ad mixture" for this option
