Barricaded

Reach 999 Block in one combat - the big brother of Impervious. You really want Barricade (Ironclad; block no longer expires between turns) so your block accumulates, then pile it up over several turns with block cards - Body Slam decks live here. Entrench (doubles current block) is the accelerator: a couple of Entrenches on a healthy total rockets you to 999. Do it against a high-HP enemy or boss that can't punch through the wall. Watcher and Defect can stack silly block too, but Ironclad Barricade is the classic.