Of all the monster templates that are published, be by Paizo themselves or by 3rd parties, which one would you consider the most uncontrollable or that you can lose control pretty quickly with it?
For me [so far], the template that can lead to brokeness is the Undead Lord from Sword & Sorcery's Tome of Horrors Complete Unlimited Edition. Why? Basically, it's your typical enhanced undead template... until you read this part:
Create Spawn (Su): A creature slain by an undead lord rises in 1d4 minutes as an undead creature of the same type as the undead lord. Spawn are under control of the undead lord. This replaces any other create spawn ability the base creature possesses.
Applying it to a ghoul, a skeleton or zombie, no problem...
Applying it to a ravener... or a lich... or worst, such as Agmazar the Star Titan, y'know, ANY undead that can one-shot-kill an entire settlement? What would happen if an ravener undead lord wipes a village with its breath weapon? You would get a flock of raveners in no time. Ouch...
So yeah, while the Undead Lord is great for powering up weak undead, it's not so great for greater ones when they can turn every victim into their own powerful selves, under THEIR control.