MU is one of your best characters, and you want to demote him to a rallybot? Shameful.
Just an FYI, every character in the game has an Asset and a Flaw.
Yes, but you can't pick the asset and flaws of other characters, and most of the other characters don't have MU's potential to be god-like. --- "I used to be an adventurer like you, but I took an arrow to the knee." - Whiterun Guard
Of course, it is entirely possible to keep the rally bot in the log book for instant access in other save files. --- Why are Lucina and Owain companions oh **** what I used Lissa so little I forgot she was part of Chrom's family
To get back on topic, I'd say something with high defense and resistance, with low strength and magic. The rallybot won't be doing damage anyway. --- "I used to be an adventurer like you, but I took an arrow to the knee." - Whiterun Guard