You would be able to deploy a Taskmaster on the Howdah at the beginning of the game, even if the rappelling lines no longer allow you to ascend into it. The Fallen Realms sourcebook says only that 'models' from the following army lists can be deployed in the Howdah - not warriors or heroes.

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http://napoleonicstrategybattlegame.yolasite.com/

No, it specifically lists the available warriors that may be deployed in the howda as part of the mumaks warband.

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"Draw your sword with a heavy heart, but swing it with a heavy hand"

maybe the gw thought that giving free potential might to the commander would make the mumak a bit to powerful.

Absolutely

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BLACKHAWK 2010 2013 2015 DYNASTY

1) Can the Fight Value of a Mumak Commander (who has called a Heroic Strike) be used by the controlling player in a Fight the Mumak is part of?

I would say yes. The rules explicitly state the Mumak is the Commander's mount (Harad & Umbar 32). Cavalry models are allow to mix and combine the statline of the rider and the mount (ie. Warg Riders using the warg's strength instead of the Orc's). All the FAQ says is that the Mumak does not follow the rules for Monstrous Cavalry.

2) Can a Haradrim Taskmaster's Whip of the Master's Special Rule affect the Mumak's Commander and/or the Mumak itself?

I would say no. The range is 6+ and ranges are always measured as "base to base." Case in point, the rules state that only the Commander's heroic actions may affect the Mumak "...even though its base is more than [6"] away" (Harad & Umbar 33). This seems to imply that ranges, even when measured vertically, are still "base to base." Whether using a regular Mumak Commander of the Mahud beast master, his base will still be more than 6" from a Taskmaster on the ground

However, if you have a very interesting board with elevated terrain, such as a situation where the Taskmaster is in a tall tower, then it may be possible that the Mumak Commander is in range.

Now as to the Taskmaster affecting the Mumak itself, this would only work if the Mumak had might of its own which it of course does not. The Commander and the Mumak are not treated as a singular model in this case.

So in sum, yes on the Commander's Heroic Strike, no to the Taskmaster.