There are many reasons why your bonus may not be working.
Stop bonus in either an ability or a bonus (Nitemare)
You may be playing in a room that is random. This means that unless you have double their attack then its always a shot in the dark if you win or lose. You just have a better chance if you have more attack.
does it show the -10 min 3?
or does it display an X over it?
or does it display None in the bonus area?
Because if you ask me, i think your bonus is working.
it just doesn't show the -10, because it's Attack related, not Power.
and the cards don't display the Attack, only Power.
the rest you have to do on your own using Basic mathematics.
Power is on the card, each card displays Power and Damage. so Lamar has 6 power, and 8 damage at level 5.
the card will display those two values only...
but, it also displays an ability, and a Bonus.
in Lamar Cr's case, Ability is stop Opponent bonus.
and Bonus(active only if two or more cards from the same clan are in your hand)
Lamar Cr's bonus is -2 opponent Power min 1.
so, if Lamar goes up against Lyse Teria Cr, power 8, damage 4.
Ability stop opponent ability.
Bonus - 12 attack min 8(only active with two or more cards from the Montana Clan in your hand)
so, Lamar will have 6 power, and 8 damage on the card when in the battle round(showing the attack animations)
Lyse Teria will have 6 power(because Lamar Cr's bonus reduces Lyse Teria Cr's power by 2)
but, if Lyse Teria Cr uses 3(+1 pill as a base) pillz, she will have an Attack value of 24, 6 times 4 pillz.
if Lamar Cr uses 4 pillz(+ 1 for base) will have 30 attack, 6 x 5 pillz. but since Lyse Teria Cr has the bonus active, Lamars Attack will be reduced by 12, leaving Lamar with only 18 attack.
so in conclusion.
Power, and Damage are shown.
and the Number of pillz you use are shown( + there is one for a base pill, which doesn't take away from your 12 to use)
but your Attack is not shown, and must be calculated Manually, or with an outside program.
so, anything that reduces attack, or adds to attack are not shown.
but anything that affects Power, or damage, or bonus, and Ability will be shown.