The Welcome Badge in Slap Battles appears to have been around at least by July 31, 2022, based on a public video specifically about getting that badge.

What I could verify

  • A July 31, 2022 video is titled “How To Get Welcome Badge In Slap Battles!”
  • That gives a firm latest-known public reference point for the badge’s existence, but not necessarily the exact day it was first added.

Best answer

  • Known by: July 31, 2022.
  • Exact add date: not confirmed from the sources I could verify here.

Quick note

If you want the exact badge-added date, the best source would usually be the game’s badge history or an archived patch note, but I can only confirm the date above from the available public record.