One way you could do it would be to make a new event page for each NPC that will be affected by the invisibility effect. So for your chasers, they would have the normal page where their movement is set to approach, then another page where their movement is set to random or something, how they should move when the player's invisible. Then for that page have the condition set to a switch called something like IsInvisibilityOn, whichever one gets turned on when the player equips the invisible effect. Hope this makes sense!!