Channeler Initiate Channeler Initiate is a mana dork that adds mana of any color, and it has three uses
However, it is important to mention that you are not really gaining any tempo from this trade, since when you take a card from your opponent's hand, they are never spending their mana to cast it (unlike a Counterspell, for example, which has a weird Time Walk effect on the opponent, since you not only stop the spell but also force your opponent to spend mana attempting to cast it)
Theres a good chance combo decks would only get better with more tutor options at their disposal, too
Every single zombie you play will shrink opposing creatures
Tarmogoyfs holding a guy Tarmogoyf is probably one of the most looked-at Magic cards of all time, but that doesnt mean its actually seen
Sylvan Library Speaking of multi-format staples, Sylvan Library can even make the cut in Vintage, besides being often seen in cEDH