<p>Yes, fiend creatures are affected by loot bonuses such as Double Loot events as it was stated on the second teaser's TD;DR:</p><blockquote><p>The loot chance of dust is independent of any kind of loot bonuses. <strong>Slivers however benefit from loot bonuses.</strong> Without any bonuses, fiendish monsters drop three to seven slivers.</p><p>—<a rel="nofollow" href="https://www.tibia.com/forum/?action=thread&postid=39250946#post39250946">Post #39250946</a></p></blockquote><p>Such information was also referred to on the announcement of the upcoming Double Loot event, however it did not specify which resource would be affected by the upcoming double loot event:</p><blockquote><p>This it:</p><blockquote><p>This combination will also come in handy for those of you who want to farm resources which are needed for upgrading items via the Exaltation Forge.</p><div>—</div><a Forge.</p><p>—<a rel="nofollow" href="https://www.tibia.com/news/?subtopic=newsarchive&id=6451">News: Double Loot & Rapid Respawn Weekend</a></blockquote>Weekend</a></p></blockquote>