Forgotten realms. Elminster series

Elminster the mage returns for more adventure and magic in this second installment of his travels through the Dungeons & Dragons’ Forgotten Realms
It is the time of the great elven city of Cormanthor, when the Heartlands are home to barbarians, wicked dragons rule the skies, and the elven people trust no one. Wizards and warriors alike threaten their civilization in vain, arrogant, and ignorant quests for glory.
Thus it...

Elminster the mage descends into the depths of Hell from which it will take all of his powers to escape
When an ancient evil banishes Elminster to the depths of the Nine Hells, his earthly powers diminsh, reducing him to one of the many lost souls of the inferno. Elminster, Sage of Shadowdale, Chosen of Mystra, faces his most desperate struggle yet—to remember himself and to cling to his very sanity—
as all of the forces...

The once-immortal Elminster Aumar faces old age and old enemies in this epic first installment in the Sage of Shadowdale series
 
The great mage Elminster is now an old man, surrounded by enemies and dreaming of the noble adventures of his youth. Once a wizard more powerful than any other—immortal, and beloved of the goddess of magic—Elminster’s world was torn asunder by the murder of Mystra and the mayhem of enchantments...

Commanded by the vestige of Mystra to work together, Manshoon and Elminster engage instead in a ferocious battle that sends the Sage plummeting into the Underdark as a cloud of ashes. Elminster soon inhabits the body of a fallen dark elf, so that he can begin carrying out Mystra's orders to rally Cormyr's Wizards of War, seek blue flame items to mend immense rifts throughout the realms that are releasing deadly monsters, and prevent the ancient Primordials...