Knightfall
World of Kulan DM
A natural one will mean Tim hits the portal instead of the doppelganger.By the way, I am hoping that if all the other spellcasters (including the young mage with the wand) can now pepper the Doppleganger with several "auto hit" spells, that there won't be much need for further blade-play near the circle.
@Knightfall how bad would one need to miss a nearby target in order to have a chance of striking the circle?