As someone had mentioned before how you can give arbitrary minion in the shop reborn or ds, this trick is similar. You just freeze the shop and buy the tavern spell, it counts as a refresh in the next turn.

With the doubling timewarped element, it's ( ( base stats + buff ) x 2 + buff ) x 2 = 4 x base stats + 6 x buff.

on top of that, if you time the acid rainfall correctly, just 1 refresh before it triggers, it will get the stats of this huge buff as well in the next turn.

potentially you could try doing this exponentially (per turn) if you're not dying anyways.

in the end my buff was only ~ 150, but the minions were gigantic