"Holy Shit!" Quotient: The Timurids bring nine thousand troops into Scotland, totally dwarfing any army that could be assembled against them. Except the fifteen thousand Scots waiting for them.
Magnificent Bastard: Aodh Canmore, full stop. Pick one of his plots, any of his plots. From destroying the Moors while Domnall is incapacitated to convincing Domnall to attack the Danes to convincing Hungary to invade and sack Rome and then retaking Rome and talking the Pope into surrendering control over all the Papal lands to Scotland to the entire false Downer Ending that leads to the simultaneous assassination of the entire Timurid leadership, Aodh Canmore is someone you do not want to try to out-fox.
Fearghus Campbell and his successors in the Scottish Spy Network also serve as these. Even after two full generations of new Spymasters have replaced him, people all over the world still get the creeps when his name is mentioned.
Gille Calline the Balleol deserves a mention too.
Memetic Badass: Angus the Mauler. A Danish commander is perfectly sure that they can put up a good fight against the Scots... and then learns who their general is.
Fearghus Campbell, the first of Scotland's spymasters, is still feared despite being dead.
Aodh forges documents framing Denmark for causing the excommunication of Scotland, incensing Domnall enough to start a war with Denmark. He does this because he felt that the new found peace was weakening Domnall and making him lose respect amongst his people. For the record, this act leads to an unmitigated, one sided genocide of the Danish people, and he did it because he felt his King was getting soft without a war to fight.