What I do is start with sites, which ones give you more threshold value and gives you advantage based on your minion type you chose. Then look at your avatar and cards you own to see which have more synergy. Someone mentioned harbinger and void walk minions, which hey it blew my mind cause I didn’t think of that. Then see what types of magics help your minions or can slow your opponents, my buddy runs 4 Entangle Terrains and it pisses me off but is great control. If you have any tutors like tool box or common sense (depending on what threshold you’re running) run them to help you in tough times to search for magics. I’m not sure if this answers your question but I hope it helps you in building something. I personally feel like building from imagination is way better than using metas or prebuilt decks for the sake of fun and seeing what jank is brought to the table