... Then I noticed you requested "slashing" sprites as well... Not sure if "slashing" with Yoshi's tongue would actually make sense! "Roundhouse Lick", maybe! ... I dunno. Maybe should scrap this idea because Yoshi's tongue is for swallowing enemies, not hurting them.
Besides, I once made concept art for a Yoshi adventure game, during which Yoshi is given a sword and shield at a castle. In my eyes, it's not that far off of a concept to give him a sword!
Now that I think of it, there was a Mario tileset that had the hookshot as Yoshi's tongue, ... but I think the non-scripted hookshot uses the regular Slash sprites, so maybe that wouldn't work. ...