Eleven BOROBORO reactions, free. Transparent PNGs at the exact sizes Telegram, WhatsApp and Discord ask for, so they upload first time. No sign-up, no email, just take them.
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HOW TO USE THEM
Telegram — take the 512 set. Message @Stickers, send /newpack, name the pack, then send the PNGs one at a time as files, each with an emoji. Telegram wants 512×512 with a transparent background, which is exactly what you are downloading.
Discord — switch to the 320 set above; Discord accepts nothing else. Server Settings → Stickers → Upload. Needs a level 1 server or higher.
WhatsApp — take the 512 set and open it in any sticker-maker app. These are already square and transparent, so the app only has to convert to WebP.
X, Slack, anywhere else — either set works; just attach the PNG like a normal image.