Getting Powerful Monsters Early

With really quite modest amounts of effort, you can get Rank A and Rank B monsters before you've set foot anywhere where Rank D monsters spawn.

Great argon lizard

The great argon lizard (Rank B Dragon) is synthesised by a quadrilineal synthesis of four argon lizards (Rank F Dragon). You can find mid-teens argon lizards (and, for that matter, great argon lizards) on the "Dragon" type of uncharted island, but you can also synthesise them quite easily from the wild Rank F monsters that can be found on Infant Isle and Xeroph Isle.

The following syntheses can produce an argon lizard from wild Xeroph/Infant monsters in one step:

Frou-frou

The frou-frou (Rank B Dragon) is synthesised by a quadrilineal synthesis of three frou-fry (Rank F Dragon) and a great argon lizard. You can find mid-teens frou-fry (and, for that matter, frou-frou!) on the "Dragon" type of uncharted island, but you can also synthesise them quite easily from the wild Rank F monsters that can be found on Infant Isle and Xeroph Isle.

The following syntheses can produce a frou-fry from wild Xeroph/Infant monsters in one step:

Drakularge

The drakularge (Rank B Dragon) is trivially synthesised from a frou-frou; just about any old thing you synth with a frou-frou will yield one.