Custom reactions for Slack. Generally optimized for resolution and filesize (i.e., these will all upload to Slack out-of-the-box).
These are images that I thought would make good Slack reactions, but had to manually rescale because of Slack's 128x128 resolution limit and 64K file size limit. I'm putting them here in case anyone else wants to use them but doesn't want to go to the trouble of having to edit an image down to 128x128 in $CURRENT_YEAR.