It is was a tedious task to mention users: copy, type, paste. This script makes it a single step: drag and drop any username on to the comment you're composing, and tada! It's there.

Here is the script:

// ==UserScript==
// @name     tildesDragNDropUsernameForMention
// @version  1
// @grant    none
// @namespace   tildes.net
// ==/UserScript==

var userLinks = document.querySelectorAll('a.link-user');

var dragstartHandler = function (event) {
  var text = event.target.innerText;
  if(!text.startsWith('@')){
    text = "@" + text;
  }
  event.dataTransfer.setData("text", text);
  event.dataTransfer.dropEffect = 'copy';
}

userLinks.forEach(function (each) {
  each.setAttribute('draggable', true);
  each.ondragstart = dragstartHandler;
});

Patches welcome!

Edit: remove useless code

For those who want to prolong the experiment, here is a userscript to help:

// ==UserScript==
// @name     tildes
// @version  2
// @grant    none
// @namespace   tildes.net
// @include     https://tildes.net/*
// ==/UserScript==

document.querySelectorAll('.is-comment-mine .comment-votes').forEach((v) => v.parentNode.removeChild(v));

['.btn-post-action[name="vote"]', '.btn-post-action[name="unvote"]'].forEach((sel) =>
  document.querySelectorAll(sel).forEach((b) => b.innerText = b.innerText.replace(/ \(.*/, '')));

I am fairly sure that this syntax requires ES6, so if your browser is not compatible, you need to reimplement this using ES5. Should be straightforward but a bit more verbose.