Lotleth Troll

The discard cost is the whole engine, and it points the card at a deck that wants its creatures in the graveyard rather than on the battlefield. Most aggressive two-drops grow by drawing more gas; this one grows by throwing gas away, which turns a hand full of dead creatures, flashback fodder, and reanimation targets into a clock. Each discarded creature is a +1/+1 counter, so the card converts cards you no longer need into combat damage at no mana, and trample makes that accumulated size land instead of being chump-blocked away. The regeneration ability is what keeps it on the table while it does this: a 2/1 body grows fragile to removal the moment it matters, and one black mana buys it past combat and most targeted spells, leaving sweepers as the clean answer. The synergy with self-mill and reanimation runs both directions, since the creatures you pitch to pump it are often the ones you most want in the yard anyway, so it has always belonged to graveyard-centric black-green strategies rather than fair midrange. It is a rare aggressive creature where filling the graveyard, growing the threat, and feeding the recursion plan around it are the same action, and the cost it pays for that efficiency (handing you a body that demands cards to grow and mana to survive) is exactly the cost a graveyard deck is happy to pay.