If I had one piece of advice to highlight, it would be to always have a lower-power deck available to help people test their own lower-power decks
I may also add that Courser with Connections is messed up crazy bonkers like wow
Dryad Arbor Dryad Arbor is both a land and a creature, but it isnt a spell
You love to see it: niche tribe support
Lastly, there are some assassin cards that tie into specific non-assassin themes such as Lys Alana Scarblade in elves, Goblin Assassin in goblins, Silent Assassin and Rathi Assassin in mercenaries, Unliving Psychopath in zombies or equipment decks, or Hunter of Eyeblights and Massacre Girl, Known Killer in -1/-1 counter decks
Youre selecting synergistic cards that are in many cases among the best of those effects (if not the best), and youre moving away from theme and closer to just making your deck the best it can be