Stensia Plane: Innistrad Whenever a creature deals damage to one or more players for the first time in a turn, put a +1/+1 counter on it
This article explains the rarity structure, how to identify them, and the characteristics of popular cards that fetch high prices in the market
And while it may be fun to play fetch with Pako, Arcane Retriever, its not of much use unless you partner it with the mono-blue Haldan, Avid Arcanist
Additionally, if your deck has a lot of card draw or even just manipulation (your Commander Scrys or draws, for example, or you're Mono-Blue with a ton of cantrips and Ponder-style effects), you can adjust your number
I use Balance in my Cube and it performs as one of the most overpowered White spells