Sheet 0 is not an SFX, but a Marching Tuba Bassline
Sheet 1 is a Telephone tune
Sheet 2 is a Shotgun
Sheets 3 & 4 are not an SFX, but a F# turnaround
Sheet 5 is a Battleship Cannon
Sheet 6 is a Toilet Flush
Sheet 7 is not an SFX, but a test on my Vibraphone
Sheet 8 is a sheep
Sheet 9 is an 8-bit SFX (idea from Icebolt)
Sheet 10 is Carrot’s Heartbeat effect (everyone uses it)
Sheet 11 is a Cell Phone sound
Sheet 12 is not an SFX, but THEFinalBoss’ favorite key: B major
Sheet 13 is not an SFX either, but a test inspired on Nuselline’s Utopia
Sheet 14 is even not an SFX, but a test with Synth #2
Sheet 15 is either not an SFX, but a Low A string test on Electric Guitar
Sheet 16 is a Blowing Spaceship
Sheet 17 is not an SFX, but a Test with low Piano #1 chords
Sheet 18 is not an SFX either, but a Techno inspired Mute guitar
Sheet 19 is even not an SFX, but an End test

Credit to Alienz & Kabob340 for the SFX ideas too