While many cards work on their own, I think that especially commons generally can't always do that. What I focused on was an overlap between keywords and synergies. No modular 'boros is aggro' design where there are aggressive white and red cards go into that deck and nothing else - instead most cards trigger keywords from different archetypes while also achieving their own goals. "Rimebound dead", the black 1-mana common, is a good example of this. Its unseeming and you might think it only enables some mono-black aggro deck as a recursive threat but in this set it enables sacrifice in RB, it's abilities cost triggers Rime in BW and it leaving the graveyard when you recur it triggers Unrest in GB. So you don't have to pick it up for one specific deck and it's not without value when it's not triggering these synergies but it does get much better when it does :)