I've always loved the Illusionist class, and GuildWars 2 does a good job of capturing some fun mechanics that can be incorporated in Oblivion Remastered.
The Mesmer has a few special gifts. Here are a few thoughts on how they can be incorporated:
The player can produce clones of themselves (ones that appear exactly like the user, and ones that are slightly altered).
Spell to summon a lookalike of the player, with the same weapon/armor.
Spell to summon a similar looking player, with various weapons (rotating weapons, or various spells for each clone type), and a purple glow.
The player can summon a clone when blocking.
It would be neat if it were possible (for the player only) to summon a clone upon blocking -- one that lasts only a short while.
The player can teleport, or create mini portals from one spot to another spot.
The player can manipulate time on themselves, setting a point in time, incurring damage or using skills, then reverting to the state they were in at that point in time (a few seconds later).
The player can summon illusionary daggers to strike the foe, flying like arrows toward the enemy.
The player can cause confusion in the mind of their opponent, making them see phantom images of their worst fears.
I'd love to see what you guys could do with some of these.