any number of cards named mtg Templar Knight (Foil Etched) A deck can have any

Lets use Errant Ephemeron as an example

But how does the set play

Any choices made on resolution, such as whether to put counters on a permanent, are also made individually.

At the right power level you get efficent threats that just happen to bring along a lord who rewards you in a big way for having a bunch of the same creature type on the board

The other downside to this one is that unless you can remove it, you are obligated to pay the life and draw a card, so it is possible to lose to your own Phyrexian Arena

More than just because Seven is thematic, its also because the deck out of the box performs quite well already