For the ear ringing… i would, until you can make you own sound that you could package in your game, grab a similar sound by using a “youtube → mp3” website, then using Audacity to make the mp3 a wav, then import that into UE4 and build a sound cue out of it.
For the explosion effect, i’d start by going into the content examples, finding an explosion, and altering it. It’ll teach you how to mess w/ particles and you might be able to tweak it into something you can use.
Then I think you’d add all of that into the Boss Actor’s Blueprint. The Explosion Particle effect would be added to the components, set “auto activate” to off, and then when he’s defeated it would turn on and run once. Same with the sound.
I think! I’m kind of new at this too, just trying to be helpful!