Sever, just because he's an illusionist doesn't prevent him from casting not illusionary spell like Stoneskin and Meteor Swarm.
Being an illusionist just prevents him from casting spells from the opposite school - Necromancy.
Now, for his stats.
He is a level 18/20 Gnomish Fighter/Illusionst.
STR 18/89, DEX 18, CON 16, WIS 8, INT 10, CHA 8.
129 HP, 3 attack per round.
Saves 2/4/4/2/1.
Anything else?