Seed: -6799847691154819072
With this first seed, you will spawn in the mid-sized swamp surrounded by several other biomes, like desert, plains, and savannah.
Seed: 7394116204989160085
The second seed is a little more special. Right in the middle of the Mangrove biome, there is a big chunk of the Plains biome. It looks like a lonely island, but it also can be an opportunity to build a cabin here.
Seed: 1305619067429899667
Finally, last but not least is a seed featuring a village concealed in the Mangrove. Such village generation is most definitely not intended by the developers, judging by the look of it.
Frogs can be found in that biome.