Back before I wrote articles for Pojo, I was a big fan of other people's articles on Pojo. My favorite was Judge Bill's Corner, where he'd answer questions about various rules and card interactions. He's not writing those anymore, sadly, or else he may have caught a mistake I made in a recent article.
Fortunately, Andrew happened to catch it and inform me. Here's what he had to say:
You mention in a recent deck garage post that a problem with Verdeloth is that playing him with Leaf-Crowned Elder means you don't get to pay kicker. Actually, kicker is an additional cost when you play a spell, and Leaf-Crowned Elder has you play a spell, so actually when you flip him over you get to pay a lot more for kicker than normal.
Side note: This also means that cards that increase the cost of playing spells (Sphere of Resistance, for example) make you pay additional mana to use Leaf-Crowned Elder's kinship ability. This is also true for other alternative methods that mention playing spells (Flashback, pitch spells like Force of Will, etc.)
So I looked it up on Gatherer, and sure enough, playing a card off of Leaf-Crowned Elder's kinship trigger will in fact allow you to pay any extra costs, like Verdeloth's kicker, without paying the actual mana cost. And cards like Sphere of Resistance will make card splayed this way cost more.
Andrew isn't completely correct though. According to the Oracle rulings, if you play a card this way, you can't pay any alternate costs. So if you could somehow play Force of Will this way, you wouldn't have the option of discarding a card and paying 1 life-- you'd have to play it for its mana cost, which Leaf-Crowned Elder says you don't have to pay.
Force of Will isn't a Treefolk card or a Shaman card, and currently in Magic there is no way to make it one. There are creatures with alternate costs, however, and Conspiracy could make such creatures Treefolk or Shamans even when revealed off the top of your library, so the situation could in fact come up. You couldn't, for example, use the Elder to play a creature with morph face-down, because that's an alternate means of playing the card.
If any of you ever see a similar mistake in one of my articles, don't hesitate to let me know.