Cheapest priced copy (Foundations Commander): $0.49 at Card Kingdom, near mint, their price list as of .
Tyrant's Familiar 
Creature — Dragon · 5/5 · Rare · Foundations Commander · #183
Flying, haste
Lieutenant — As long as you control your commander, this creature gets +2/+2 and has "Whenever this creature attacks, it deals 7 damage to target creature defending player controls."
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
5 printings · $0.49 to $2.29 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2014 | 39 | Rare | $0.79 | — |
| Commander 2017 | 143 | Rare | $1.49 | — |
| Commander Anthology Volume II | 125 | Rare | $2.29 | — |
| Foundations Commander | 183 | Rare | $0.49 | — |
| Starter Commander Decks | 165 | Rare | $0.69 | — |
5 rulings from Wizards of the Coast
- 7 November 2014If you lose control of your commander, lieutenant abilities of creatures you control will immediately stop applying. If this causes a creature’s toughness to become less than or equal to the amount of damage marked on it, the creature will be destroyed.
- 7 November 2014Lieutenant abilities refer only to whether you control your commander, not any other player’s commander.
- 7 November 2014If a triggered ability granted by a lieutenant ability triggers, and in response to that trigger you lose control of your commander (causing the lieutenant to lose that ability), that triggered ability will still resolve.
- 7 November 2014If you gain control of a creature with a lieutenant ability owned by another player, that ability will check to see if you control your commander and will apply if you do. It won’t check whether its owner controls their commander.
- 7 November 2014Lieutenant abilities apply only if your commander is on the battlefield and under your control.