How can I make mob spawns other mobs around?

Use a timer to limit the spawns. Tracking the ticks inside the "on entity tick update". When said ticks reach a certain point (like 100 ticks, which is 5 seconds), then allow it to spawn a custom mob. Or you can use the random integer block to make the spawn random.

Can you make a screenshot pls?

i need help with this too, i need someone to send me a screenshot or explain to me how to make my boss mob spawn another mob

I also need help with this xd

except I want it to be done if the mob sees the player sometimes