Played mercenaries for a while, quite a nice experience so far. One issue that bugs me and many people is that there’s no way of undoing upgrades. Yes, someone would say the description is right there, why didn’t you read beforehand? But it’s not about whether to read the description or not. No one can read and remember all the mercs abilities at the beginning, leave alone all the potential fun synergies and combos. For some abilities that change the speed, it is quite reasonable to see people upgraded it during leveling and permanently lost the opportunity for some interesting combos, which are one of the most interesting parts of this mode. Maybe unlimited undoings are too aggressive, but at least we should have some way of doing it, say, half coins refund, or even no refund.
An even better approach than simple undoing is just to give players the ability to choose the rank, or a combination of stats of a merc ability at different ranks, so that we can keep +1/+5 at maxed. And I do not think these changes are very difficult to implement nor incompatible with current mercenaries UI overall.
Some examples:
Velen third ability: velen’s blessing
Mutanus third ability: Devour
Many more…