@DEADP00L - love your idea, but I wanted to take it a step further - which makes it more efficient AND consolidates the concept, enabling it to be broader in scope.
Many people have millions of tavern silver "coins", and I know personally I'd like to use them more often for game value, but so many of the items don't fit at all.
Again, many were created back in the early game when they might have had appeal, but sit dusty, dormant, and unloved by today's players. They're anachronistic. Merchant offerings *really* have a lot of dust, for sure.
I know it's getting unsafe to suggest anything because it could be:
1) Fragmented or diluted in value
2) diamond-costed or cash-costed
But Pandora didn't let HOPE out of the BOX, so maybe we should keep trying too.
I created a small UI screen to demonstrate the concept here of Purchasing ATTACK in the NEW tavern shop! I didn't get fancy, but tried to hit the BIG points (didn't do any graphics, either)
1) ARMY TYPE is pretty clear - a single group control defines BOTH of the choices you can make, once at a time of course

2) In this new idea, INNO populates the
% and
duration drop-down lists with valid choices of integer values. PS: There are lots of control types - it doesn't have to be a drop-down list, it could be a slider control, etc.
- Attack % (0 - 100 for %), so can be anything between there (integer value): 11, 26, 63, 84...
- Hours (1-24) for duration although that could get more granular (for example, 15 minutes choices, under 1 hour)
3) In other words, the user can choose
their needs of BOTH power and time, from a range offered in the drop down boxes.
Each combination generates a cost, and the user can then choose to activate or go back to lower or raise EITHER determinant, which will raise or lower the cost - until they like it and/or can afford it - before finally accepting it via the "ACTIVATE" button.
Same rules can of course apply as they would in the current tavern:
You can't stack multiple attack items or choices in the tavern, for either offense or defense.
That could be built into the logic of the dialog box and code processing the request.
I didn't make multiple types of UI dialog boxes, but just this one to consolidate how you could use a SINGLE box with choices to apply to ATTACK boosting multiple uses for that component.
1 Defense BOOST UI could have one very similar, too - in other words - 1 UI for ALL defense requirements. IN this image, a player has already activated her ATTACKING army defense boost, and now wants to do something to help her city defenders, which is a still available option.
In summary:
the big add here is that users can pick a DURATION and POWER pair of choices and have a custom cost generated for that exact pair - they are no longer static, as they are today.