Try the Commands Troubleshooting and Help page if you get stuff with server errors.
Minecraft Ravager NBT Data Tags
Using the summon command to spawn in a minecraft ravager is simple, take the command and enter into chat and presto you have a ravager. Ravager generally spawn as part of a raid, they have a number of cooldowns timers that delay there actions each cycle.
Make Ravagers attack more or less often, (or roar, and stun less often)
The AttackTick, RoarTick and StunTick will occur with the same delay each time (20 ticks are 1 second). The attack/roar/stun will still take the same amount of time, and it only the time delay between being allowed to do that action again
In this example, the Ravager would be lucky to get an attack before being killed.
/summon minecraft:ravager ~ ~ ~ {AttackTick:1000,RoarTick:1000,StunTick:1000}In this example, the Ravager will attack often and but will not roar or stun before quite some time has passed.
/summon minecraft:ravager ~ ~ ~ {AttackTick:10,RoarTick:100000,StunTick:100000}Illager Patrols
Setting Patrolling:1 and PatrolTarget coordinates will make illagers to move towards the patrol target.
/summon minecraft:ravager ~ ~ ~ {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:ravager ~ ~ ~ {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.