I did these concepts while following the VFX Apprentice Course (https://www.vfxapprentice.com). I invested a lot of time, research and iterations and you can follow the whole process and many WIP images in this thread: https://realtimevfx.com/t/simon-trumpler-vfx-sketchbook/4177/115?u=simonschreibt
The course teaches how to draw vfx concepts for an explosion, slime, smoke and lightning. On this image you can see the concepts given in the course (as you can see, with my images I deviated quiet a lot from the course goal): https://kajabi-storefronts-production.kajabi-cdn.com/kajabi-storefronts-production/themes/3160642/settings_images/NhrQx3EPQkSNvgPrrxhI_Thumbnail_00d.png

Here you can see the concepts from the course (https://www.vfxapprentice.com/booms-and-blasts) which are thaught.