Cheapest priced copy (The Lost Caverns of Ixalan Commander): $0.39 at Card Kingdom, near mint, their price list as of .
Stonybrook Banneret 
Creature — Merfolk Wizard · 1/1 · Common · Morningtide · #51
Islandwalk (This creature can't be blocked as long as defending player controls an Island.)
Merfolk spells and Wizard spells you cast cost {1} less to cast.
Legal inCommanderModernLegacyVintagePauper
Not legal inBrawlStandardPioneer
3 printings · $0.39 to $17.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The Lost Caverns of Ixalan Commander | 173 | Common | $0.39 | — |
| Morningtide | 51 | Common | $0.69 | $17.99 |
| The List | MOR-51 | Common | $0.99 | — |
2 rulings from Wizards of the Coast
- 1 April 2008The effect reduces the total cost of the spell, regardless of whether you chose to pay additional or alternative costs. For example, if you cast a Rogue spell by paying its prowl cost, Frogtosser Banneret causes that spell to cost {1} less.
- 1 April 2008A spell you cast that's both creature types costs {1} less to cast, not {2} less.