Try the Commands Troubleshooting and Help page if you get stuff with server errors.
Minecraft Evoker NBT Data Tags
Using the summon command to spawn in a minecraft evoker is simple, take the command and enter into chat and presto you have an evoker.
How to set the Evoker's spell cooldown
Evokers cast a number of spells, this spell casting ability has a cool down timer known as SpellTicks. When set to a positive value it will tick down (20 ticks per second). When reaching zero the Evoker can cast a spell.
/summon minecraft:evoker ~ ~ ~ {SpellTicks:200}Illager Patrols
Setting Patrolling:1 and PatrolTarget coordinates will make illagers to move towards the patrol target.
/summon minecraft:evoker ~ ~ ~ {Patrolling:1,PatrolTarget:{X:100,Y:65,Z:400}}
Add a patrol leader PatrolLeader:1 to allow for players to receive the Bad Omen status when slaying the patrol leader.
/summon minecraft:evoker ~ ~ ~ {Patrolling:1,PatrolLeader:1,PatrolTarget:{X:100,Y:65,Z:400}}
Illager Raids
Unfortunately setting the raid tags doesn't seem to create a raid, maybe someone would be able to work these tags out.
Suggestions or found a bug
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If you're looking for a particular summon mob generator you can link to these specific versions of the command generator.
Detailed Mob Generators
Generators with pattern selectors
Other Mobs NBT Tag Data
Summon mob page with notes about custom mob options.