Do you struggle to recall what has roots nobody sees and is taller than trees? Does Gollum keep murdering you because you can't figure out what thing all things devours? Do you, in short, get frustrated by Dungeons Deep and Caverns Dim, aka the Riddle quest? If so, then one of my four riddle decks may be the answer you've been looking for, being mono-sphere decks built primarily for consistency but still with a good selection of cards. You may find these decks actually make the quest a bit too easy.
These decks were built back in November 2014, so they could definitely be improved by the addition of some more recent cards, and indeed by me having more experience deckbuilding now.
I talk a bit more about the decks and the riddle mechanic in this blog post: https://wardenofarnor.wordpress.com/2015/11/10/breaking-the-game-dungeons-deep-and-caverns-dim/
There's also a link there to a youtube video where my brother and I beat the quest using the Spirit and Tactics decks, which are probably the best two.
The general principle is simple: when answering riddles, they ask for sphere, cost and type, so you always name Tactics, 2, and ally. The Tactics deck is one of the most reliable along with Spirit.