Lately, I have been trying to regen-fight as much as I could. (mostly in the "den of danger", as I did not want to unlock too many things yet. I'd like the visual update to move a bit further first...).
Well, I am really pleased : the previous formulas have been of great help to choose which monster to regen fight (is it possible, how many tiles will I use ?). For example, I had never dared before to regen-fight a level 6 goblin with a level 4 wizard (helped with a level-up from l3 to l4). Of course, it has been pretty resource consuming : I could easilly kill the boss, but had to leave a few level 9-8 monsters alive.
Contrary to what is stated in the first posts of that
thread, there ARE items that make regen fighting way easier in early kingdoms : BURNDAYRAZ is kick ass for this.
Basically, once you have got it and manages to use it properly, it almost divides by 2 the regeneration of the monsters (burning effect + Damages when casting divided by mana cost. Thus a level 4 wizard using it will substratc up to 1+16/5=4,2 regeneration points to its foes). But of course, exploration wise, the less remaining health to regen-fighting, the better.