If you have a spell that proliferates and you dont want to choose any permanents or players for whatever reason, you can always choose none
OP13-001 Monkey.D.Luffy and ST30-001 Luffy & Ace are also names to watch, because both show how green continues to work well when paired with red pressure and Straw Hat-style support
Or of course, use it to save a creature from removal or just re-up on a powerful enter the battlefield trigger
You can proliferate counters on tokens, but you cannot add extra tokens this way
As for our mechanical friends that introduce Prototype with The Brothers War, there are 18 in total (four mythics, three rares, six uncommons, and four commons) and appear in all five colors, so youve got your pick of options
Imagine you go to cast Coalition Victory and someone casts Swords to Plowshares on your Commander in response