It’s not a slamdunk with the three stamp attempt, because you likely won’t have enough hearts to clear the board unless you’re very careful about only spending hearts on unrevealed monsters (vs the slimes that get revealed by the slime mage scroll).
I found the best strat for the three stamp run is to restart the game (you can just press R for a quick reset) until you get a favorable starting reveal. Ideally you want the mice to limit the search area for the rat king to no more than 3 columns or, ideally, indicate the exact column it’s in. Otherwise it’s almost impossible not to accidentally click on unrevealed mice as you work your way through the board.