Okay, I've mistakenly listed this as a balance issue earlier and as a consequence it hasn't been noticed or taken into account. However, it's a real bug, and a gamebreaking bug.
If I cast Growth on a unit - instead of a single character, it doesn't give +50% attack, but much more.
Example: a unit of 5 Shields of Gilden with 60 total attack (12 per individual), once buffed with the "Growth" spell, gets 210 attack. Each individual in the unit has now 42 attack.
12 + 250% = 42. (60+250% = 210).
I ran other tests and here's my conclusion: [UnitStat_CombinedAttack] is broken. It doesn't refer to the power of an individual in the group, but to the combined attack of the whole group; however, the boost is applied to each member of the group. So a group of 7 shields of Gilden with the same weapons would go from from 84 to 378, or 54 per individual.
+50% attack is already a bit strong for 4 mana, but +250% or +350% is just ridiculous. Please fix it.