Cheapest priced copy (Jumpstart): $0.35 at Card Kingdom, near mint, their price list as of .
Sky Tether 
Enchantment — Aura · Uncommon · Ravnica Allegiance · #21
Enchant creature
Enchanted creature has defender and loses flying.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Jumpstart | 133 | Uncommon | $0.35 | — |
| Ravnica Allegiance | 21 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 25 January 2019Sky Tether can enchant a creature that never had flying at all.
- 25 January 2019The enchanted creature can later gain flying from another effect.