Eternal Witness is played by many She does see a ton of modern play
This card is essentially two Rampant Growths stapled together, because a card that costs four mana should earn you +2 extra lands
A lot of balance and care goes into choosing the cost of a card, more than I can express here, but looking for similar effects on existing Magic cards can give you an idea of a fair costfor example, a ramp spell that puts two lands into play ought to cost 4 mana, per Explosive Vegetation
It keeps all cards attached, damage counters, Special Conditions, and turns in play which opens a world of possibilities
Honorable Mention #1 - Knight of the White Orchid This lil' Knight of Mine, I want to let him shine
Yes, many Target locations enforce purchase limits of 2-5 items per person per day to prevent scalpers from buying entire restocks