Spectacle, the new Rakdos keyword, gives spells an alternative cost. You can cast a spell for its spectacle cost if an opponent lost life during the turn. On some cards, the alternative cost is a discount, a reward for hurting your opponents.

Crossing new horizons brings new opportunities to thrive. Adaptability is the key to success! The adapt ability imbues creatures with a latent power and toughness boost that can be activated with an infusion of mana.

Addendum is a new ability word. Ability words don't have any inherent rules meaning, so addendum is more of a label than anything else. It's found (mostly) on instants that have additional or alternative effects if you cast the spell during your main phase. So, if you're willing to give up a little flexibility, you are rewarded with extra potency.