Primordial Hydra

Most X-creatures settle their size when they hit the battlefield and stay there. This one's body is a clock instead of a number: whatever you pour in at the cast becomes the seed, and every upkeep multiplies it. Two counters become four, four become eight, and the trample clause arms itself the turn it crosses ten, which is to say the turn the math stops being a question of whether it connects and becomes a question of how fast. The geometry is the whole design. Linear growth (a counter a turn, a static buff) gives the defending player time to scale answers alongside the threat; doubling does not, because it inverts the relationship between turns elapsed and damage dealt. A removal spell aimed at it on turn five answers a 16/16; the same spell held one turn too long answers nothing. That asymmetry is why the card reads as patient and plays as a deadline. The 0/0 base and the at-the-beginning-of-upkeep timing are the brakes: it does no growing the turn it arrives, so there is always one window where it is merely large rather than lethal, and the opponent's entire game becomes a contest to use that window. It is the cleanest expression of exponential threat-scaling on a single card, the kind of design that needs no support to win and no text beyond three lines to terrify.