I know it isn't custom level, but you should know about it:
https://scratch.mit.edu/studios/35141809

@CodeScratcherthe1st is right about CustomDB Dev

~C-AAgBf/f0ABAAAAAAA-AAgAgCgMACAAAAAAA-AMgEf7fxAsAEAoGAAD/D/D/AA-AHgDf/gBAEAEAEAAAAA-AWgFf/f/ACACACAAAAA-AWgBf/f/ACACACAAAAA-AAgDf+gBAkAAAAAAAHi! I am grassy! I am not #Sheldon sign in desqize and other people I guess.# look at the teleporter behind you and then #go into it to start!#-AWgFf/f/ACACACAAAAA-AMgEgLgGAsAcAEAAAD/D/D/AA-AMfwgLfyAsAcAEGGYD/D/D/AA-AMgGgLfeAsAcAEAAAD/D/D/AA-AMgZgLfzAsAcAEGGYD/D/D/AA-AMgFgXfyAmAEAkAAAD/D/D/AA-
AAf5f7fkAVAAAAAAA-AAgDf7fkAVAAAAAAA-AAgMf7flAVAAAAAAA-AAgMf5flAkAAAAAAAHello! As a light, I like being a light-AAgQgBf0AsAAAAAAAABAB-AMhigEfyAoAEA0AAAD/D/D/AA-AMhigUgKAoAcAEAAAD/D/D/AA-AMhigUfaAoAcAEAAAD/D/D/AA-AAhagafdAkAAAAGMAHelp me, I am stuck to the wall! Will you help me when you find a hidden exsperamemnt that dr @grass01 has set up?-AMh1gUfyA4AcAEGSYD/D/D/AA-AMhggkfyAsAEA0AAAD/D/D/AA-AAhmgEfgAVAAAAAAA-AAhwgEfmAVAAAAGSA-AAhZgEgCAVAAAAGMA-AAhSgEf5AVAAAAGGA-AAhigKgDAsAAAAAAAAAAB-AMhNgVgCAEAgAUAAAD/D/D/AA-AMhOgVfiAEAgAUAAAD/D/D/AA-AMhNgafxAEAQAOAAAD/D/D/AA-AMg/gEfzAiAEAUAAAD/D/D/AA-AMhEgUfpAWAkAEAAAD/D/D/AA-AMg7gUf/AiAkAEAAAD/D/D/AA-AMg0gEfcAMAEAcAAAD/D/D/AA-AMg7gUfbAEAkAaAAAD/D/D/AA-AMgsgUfnAEAkAyAAAD/D/D/AA-AMg8gkf0AcAEASAAAD/D/D/AA-AMg0gkfeAcAEAaAAAD/D/D/AA-AAgxgBf7AVAAAAGJA-AAgzgKfzAUAAAAAAA-

Why still use this form? There are so many better alternatives, such as
play db (revival)
custom db (revival a part of pdb now)
robot 64+ (play db mode)
modzone something (I forgot)
robot 64 tag (private server play db level loader v2) [lets you load pdb levels and play them in tag rounds)
TL;DR just use these methods to play levels instead (the best one is probably custom DB)

Theres 2 new alternatives to this form post
Ultimate db (apart of play db revival) basically custom db but with script block
Robot xp play db (its broken but it technically lets you make and share bare bone levels)

~I-AAflh5gaABAAAAAAA-AAfxgCgBACAAAAAAA-AnflgNgaEKEKEKAAAAA-ADflgLgZAWAWAWAAAAA-AAf3f4gQADAAAAAAAAA-AAf6f+gbADAAAAAAAAA-AAfxgIgsADAAAAAAAAA-AAfngSgxADAAAAAAAAA-AAfegagsADAAAAAAAAA-AAfUgkgkADAAAAAAAAA-AAfRgkgWADAAAAAAAAA-AAfXgggLADAAAAAAAAA-AAfdgYgEADAAAAAAAAA-AAfrgIgAADAAAAAAAAA-AAf1f7gHADAAAAAAAAA-AAfkgSf/ADAAAAAAAAA-AAfSglgeADAAAAAAAAA-AAfYgegrADAAAAAAAAA-AAfrgMgvADAAAAAAAAA-AAf1gCgmADAAAAAAAAA-AAf6f6gWADAAAAAAAAA-