Cheapest priced copy (Battle for Zendikar): $0.35 at Card Kingdom, near mint, their price list as of .
Kalastria Nightwatch 
Creature — Vampire Warrior Ally · 4/5 · Common · Battle for Zendikar · #115
Whenever you gain life, this creature gains flying until end of turn.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
4 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Battle for Zendikar | 115 | Common | $0.35 | $0.49 |
| Jumpstart 2022 | 429 | Common | $0.35 | — |
| Jumpstart | 245 | Common | $0.35 | — |
| The List | BFZ-115 | Common | $0.35 | — |
3 rulings from Wizards of the Coast
- 25 August 2015The ability triggers just once for each life-gaining event, whether it’s 1 life from Drana’s Emissary or 7 life from Nissa’s Renewal.
- 25 August 2015A creature with lifelink dealing combat damage is a single life-gaining event. For example, if two creatures you control with lifelink deal combat damage at the same time, the ability will trigger twice. However, if a single creature with lifelink deals combat damage to multiple creatures, players, and/or planeswalkers at the same time (perhaps because it has trample or was blocked by more than one creature), the ability will trigger only once.
- 25 August 2015In a Two-Headed Giant game, life gained by your teammate won’t cause the ability to trigger, even though it causes your team’s life total to increase.