Cheapest priced copy (Magic 2014): $0.49 at Card Kingdom, near mint, their price list as of .
Guardian of the Ages 
Artifact Creature — Golem · 7/7 · Rare · Magic 2014 · #211
Defender (This creature can't attack.)
When a creature attacks you or a planeswalker you control, if this creature has defender, it loses defender and gains trample.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Magic 2014 | 211 | Rare | $0.49 | $0.49 |
2 rulings from Wizards of the Coast
- 1 July 2013Once Guardian of the Ages has lost defender, its triggered ability will no longer trigger when a creature attacks you or a planeswalker you control (unless it has somehow gained defender again).
- 1 July 2013The effect of Guardian of the Ages’s triggered ability doesn’t wear off as the turn ends. Losing defender and gaining trample last indefinitely.