Cheapest priced copy (Mirrodin Besieged): $0.35 at Card Kingdom, near mint, their price list as of .
Training Drone 
Artifact Creature — Drone · 4/4 · Common · The List · #MBS-142
This creature can't attack or block unless it's equipped.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
2 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mirrodin Besieged | 142 | Common | $0.35 | $0.49 |
| The List | MBS-142 | Common | $0.35 | — |
One ruling from Wizards of the Coast
- 1 June 2011If Training Drone has been declared as an attacking or blocking creature, and it stops being equipped later in combat, it won’t stop attacking or blocking.