If you controlled a creature with power 4 or greater when you declared Ruby as an attacker, it doesn't matter whether you still control one as her triggered ability resolves
When a counterfeiter have access to a high quaility printing press, things get a little harder though.
Its not like that exactly, but as I said about Mirkwood Bats, its easy to sacrifice artifacts nowadays and make this bat warlock huge
Finally, don't sleep on rituals, instants (and, rarely, sorceries) that trade a card in your hand for a quick burst of mana
Want to play an ultra-cheap Zetalpa, Primal Dawn, Zacama, Primal Calamity, or Etali, Primal Conqueror
Certainly it can free win some games