There are some strange locomotives in the world, not least articulated steam locos. OK, so a Fairlie is basically two normal locos glued back to back but American logging locos just look weird
Given that these oddities exist, what’s not to say even weirder machines could have been found? The FCPyF might have opted for a purpose built banking loco for use between Bodjio and Cumbre. Such a loco would need to have the power of two engines but need only to operate at slow to medium speeds.
This monstrosity combines the firebox/boiler/smokeboxes of a Fairlie (A) and power bogies that resemble a Garratt (B) with the V shaped cylinder blocks of a Heisler (C) turning the wheels via drive shafts and gears. The uphill end power bogie (B1) carries a rectangular water tank while the downhill end (B2) carries a cylindrical fuel tank, coal firing would not really be a viable option unless a large bunker was mounted on the boiler unit.
Will it get built? I don’t know. The banking locos currently in use (14 and 18) are perfectly well up to the job but I’ve always had a soft spot for oddball locos and it would certainly be unique.