NPC damage system

[vivid needle]

okay as you see in the pictures the npcs have just 1 type off damage, they kinda just spawn instance and it damges players that are touching the instance, what is the most effictent way to do it im thinking of adding a part to the npc model that apperas, damages players, then disappears again (using transperency) or just tell me what is the best method
second questions as you see in the video bosses has different style of attacking they start a random attack every couple of seconds how do i make that, do i make each attack in different function and keep calling them with a loop, and task.wait()

[crude cosmos]

You can use raycasts, which basically costs negligible to no lag so you could spam it with many NPCs in your world (but still, too much is bad so don't overdo it).