What are some key strategies and card choices to consider when building a competitive MTG Riddleform deck?

When building a competitive MTG Riddleform deck, key strategies to consider include focusing on cheap spells to trigger Riddleform's ability, including a mix of instants and sorceries to maintain versatility, and including cards that can protect Riddleform from removal spells. Some important card choices to consider are Opt, Shock, Lightning Strike, Dive Down, and Spell Pierce.