I read a book (or trilogy?) in the 90s about a boy who gets cut on the chest by a knife. It's a magical wound that will kill him within a few days or weeks. A good wizard assembles a group of guardian-type people to take the boy on a quest to defeat the evil ruler who marked him. One in the group is a girl with some kind of mind powers who makes the boy forget about his impending death. Another is a warrior with black eyes named Scythe after the sword he uses. The boy turns out to have magical powers as well and is eventually revealed as an elemental (?) with power over the elements.
This is "Blade of the Poisoner" and "Master of Fiends" by Douglas Hill.
The book contains an extensive discussion of elemental magic and one of the main protagonists is a character named Scythe.
Young Jarrel has suffered a wound from the evil Poisoner's blade, and is destined to die by the next full moon. Only by destroying the blade that gave him the wound can Jarrel be saved, and it will be up to Jarrel's new companions--Archer, Scythe, Mandra and the wizard Cryl-to help save him. What follows is a lively journey to the Poisoner's lair to ultimately defeat the evil-and to discover what remarkable powers Jarrel may possess.
Talents. Elementals. Good guys. Bad guys. You've seen it all before...