So Mind Control is a level 6 spell, and costs 6 spell points to include in a mind mage's spellbook. If you use it to take control of a beastmaster's falcon, you are spending 6 points to lower your opponent's spellpoints by 1 and then regain 3 spell points, the equivalent of losing 3 spellpoints to lower your opponent's spellpoints by 1. But what if the beastmaster enchanted the falcon with bear strength? then your opponent is losing 2 spell points, and you are regaining 5 spell points.
you can see where this is going. It's probably worth it to mind control a falcon if it has been enchanted with both wolf fury and gator toughness, because then you are paying 6 spell points to lower opponents spell points by 3 and then gaining back 7 spell points yourself. In other words, mind controlling a beastmaster's leverl 1 nature creature which has been enchanted with two level 1 nature enchantments is effectively increasing your spellpoints by 1 and lowering your opponent's spell points by 3. Now, imagine you're facing a warlord, and they are using an earth elemental. If you mind control it, you are spending 6 spell points to lower opponent's spell points by 5 and then you gain back 15 spell points. Effectively you are gaining 9 spell points and then lowering your opponent's spell points by 5.
Now, what if your opponent uses incantations to help increase the creature's impact on the game? Like, let's say you're facing a priestess using brogan, and you manage to bring brogan to the brink of dying, but then she uses a heal to bring him back down to 0 damage. Heal + Brogan costs the priestess 6 spell points, and it would cost you 12 spell points. If you immediately pay 6 spell points to mind control a brogan that was healed by the Heal incantation before it has the chance to use its action again, you are effectively benefiting from the Heal incantation that your opponent, the priestess cast. In other words, by mind controlling a brogan that was just healed with the Heal incantation, you are on net gaining 6 spell points and lowering your priestess opponent's spell points by 6.
A difference of 12 spell points! Imagine, that's like casting a teleport mage wand and then using it twice, only it takes 2 less actions (or just 1 less actions if you are casting it from range 2 instead of range 1, since you'll need to take a move action toward the creature to reveal the mind control).
Also, mind controlling minor creatures is a lot cheaper mana-wise, so don't hesitate to mind control minor creatures if their controller has invested a bit of resources into it.
Thoughts?
