There should be some decent UI interface when huge amounts of stacks are vacating the same spot, even if there are 2 stacks I want to see that Death Demon hiding beneath that spider! So I won't be slaughtered in the turn the Death Demon have turn after I killed the spider!

Meaby a little dot system below the stacks, that appears when there are 2 or more stacks in the same spot, that would be 1 dot for each enemy in the stack, (this way I don't even have to click the unit so see multiple stacks as per other solutions), also a way to view the secondary stacks and select them in case its your own units.

Sincerely
~ Kongdej