Springheart Nantuko With a cost this low, there's no reason not to bestow Springheart Nantuko upon another creature worth copying
Don't sleep on double strike and trample tougher as they are very powerful
However, if you've got a deck that draws a lot of cards, being able to cast spells by paying life instead of mana could be very helpful
Honest Rutstein OTJ gave Golgari a few new allies, including Honest Rutstein
As with most things in Magic, however, I encourage you to do your own research on Gatherer or Scryfall as well there are a lot of blue mass removal spells beyond those in this post, and while they will generally be the best options for many blue Commander decks, some metagames and strategies can allow you to benefit a lot from a niche effect or specialized variation
It only takes a fraction of a millimeter of deviation to cause "marked cards" to be rejected from tournament play