"Parallel Lives" is a powerful Magic card that's only been reprinted a couple of times since its initial release in the 2011 set Innistrad
Legality depends on the tournament format -- The Goose Mother can be legal in some formats and banned or restricted in others
Esper Sentinel pips both Archivist of Oghma and Deep Gnome Terramancer to a spot on this list, and its because the latter two cards both require opponents making deckbuilding decisions we cant control
A Maskwood Nexus proxy lets you run this powerful staple across every deck you own without paying secondary market prices
Kenessos, Priest of Thassa This one might be more of a sentimental favorite since dear friend, fellow RC member, and Arixmethes, Slumbering Isle designer Scott Larabee has a Sea Monsters deck, which I enjoy pulling out the Mirror Strike for
Understanding card interactions will give you a strategic edge in the game