For the AP spec, reduce the max number of points by 1, making 5 AP the new minimum for Shield Bash (or bring AP reduction per spec point down). Remove cooldown and the associated spec as well (or buff cooldown reduction to 1 turn per spec so that already existing builds won’t have to mourn the loss of spec points). The cost of each subsequent use of Shield Bash on the same turn is an arithmetic progression of base AP, going from 5 to 10 to 15 to 20, etc., with an extra condition that a killing blow incurs no increase to the AP or only half (5 > 7.5 > 10 > 12.5 and so on). Numbers could be different; this is just an example.
*inhales deeply from the shisha* and rather than being an inherent property of Shield Bash, this mechanic could be given to Shield Arm just for memes
