Transfer case low gear reduction ratios vary widely, most commonly around 2:1 to 3:1 (e.g. 2.7:1 in the standard equipment of a recent Jeep Wrangler) but there are some readily available around 4:1 (e.g. the optional transfer case in a recent Jeep Wrangler) and some more extreme reductions in aftermarket products (especially those with multiple low ratios). An entire transfer case is awkward if only one output is needed, which is presumably why Bratitude
suggested a planetary reduction gear set of the type used as either the first stage of some transfer cases (especially ones with chain drive to the front output) or as an additional reduction stage ahead of another transfer case (commonly called a "doubler"). Most "doublers" are simply the reduction stage taken from a transfer case and fit with adapters, rather than designed specifically as just a reduction gearbox.
Electric Land Cruiser
is using a BlackBox-c doubler between a Leaf motor and a transfer case
The Electric Land Cruiser EVJ80 - Nissan LEAF + Resolve-EV
One thing to watch is the input speed rating of any gearbox - to use the full operating range of the Leaf motor means a higher speed than a typical engine would ever reach. A planetary gear set can easily handle that, if the gear set and bearings and seals are designed for that speed.
Another issue is the output: doublers are intended to output to a transfer case, not to support a slip yoke (as used at the front of a traditional propeller shaft) or a flange for a CV or flex joint (as now commonly used at the front of a propeller shaft)... in other words, it doesn't have an end like a transmission tail housing.