Agree on sabertooth over lightform. Sabertooth is one of the 4 Mythic Uncommons in the set. Lightform is merely "quite good" (and normally, I wouldn't be unhappy to pick lightform second.) It's worth noting that Archfiend into either lightform or sabertooth does put us in enemy colors (which is good - we get access to high powered enemycolor common spells and we have more options if we want to go into a clan) but leaves us with strict color requirements (double color requirements in both spells)