(Warning: this guide uses light block code) I recommend you check out this guide so you can see if the boss’s gadget can hit you in the arena.
First, make a property, label it “time until attack”, make it a number property.
Next, make the arena, use an animation to make a cutsence showing the boss’s lore. Next, use custom bosses to make a cool boss look. For extra fun, layer sentries with different gadgets to make a multi-gadget-boss.
Make a small room with a barrier, make a door so the boss can’t spawn knock you out. Next, make props that last for a few seconds and then disapear, use wire repeaters to do this, and make a cycle of props, not just two sets.
Make stages, each stage is a different sentry, if a sentry is knocked out, brodcast on “knockout a stage”, add a counter that goes down each time a sentry stage is knocked out. Set the counter to start at the number of stages, and don’t make the stages respawn. Add things that happen at stages.
Make a wire repeater loop that triggers each second, add a counter paired with the property you make, make it go down each time the wire repeater “triggers”. Then, make a checker see if the property is 0, if it is 0, then reset the counter. Use a randomizer guide to choose the events. Make the trigger trigger when the check to see if the property is 0 passes.