When Toph enters, earthbend 2. (Target land you control becomes a 0/0 creature with haste that's still a land. Put two +1/+1 counters on it. When it dies or is exiled, return it to the battlefield tapped.)
Toph's power is equal to the number of +1/+1 counters on lands you control.
Toph turns your lands into a small army of beaters and scales her own power off every +1/+1 counter sitting on your lands. You ramp aggressively, animate and counter-pump lands with earthbend effects, then swing wide or push Toph through as a giant, recursive threat that returns each animated land when it dies.
Resilient board presence—earthbended lands return to the battlefield when they die or are exiled
Toph scales naturally with a counters-on-lands theme, becoming a huge threat for only three mana
Lives in mono-green, the best ramp color, so flooding the board with lands is effortless
Lands-as-creatures dodge most sorcery-speed creature removal and board wipes that target nonland permanents
Mass land destruction or 'destroy target land' effects are devastating since your threats are your lands
0/0 base animated lands die to any damage-based sweeper before counters land
Mono-green lacks interaction—little removal, no countermagic, weak to combo and fliers
Toph's power depends entirely on counters, so counter-removal or proliferate-hate blunts her
Animated lands tap or get attacked, threatening your mana base if you overextend