Landfall — Whenever a land you control enters, you get an experience counter.
Whenever you attack, earthbend X, where X is the number of experience counters you have. (Target land you control becomes a 0/0 creature with haste that's still a land. Put X +1/+1 counters on it. When it dies or is exiled, return it to the battlefield tapped.)
Toph turns your lands into a beatdown engine: ramp aggressively to stack experience counters via landfall, then attack to earthbend a land into a giant haste creature scaling with your experience. You win by snowballing huge animated lands while the safety net (they return tapped instead of dying) makes combat nearly risk-free. Play extra-lands enablers and protective trample/evasion to push damage.
Experience counters are permanent and survive removal/recasts, so the threat scales relentlessly across the game
The earthbend return clause means your attacking land comes back if it dies, making blocks and removal lopsided in your favor
Mono-green has the best ramp and land-fetching in the format, accelerating your experience count quickly
Lands-as-creatures dodges most creature-targeted sweepers since they're animated only when attacking
Board wipes that target lands or 'destroy all permanents' (Armageddon, mass land destruction) hurt your engine and counters' usefulness
Without trample or evasion, a single big blocker can wall your one earthbended attacker
Earthbend only targets one land per attack, so go-wide defenses stonewall you
Mono-green struggles with interaction—few answers to flyers, combos, or protective enchantments
Slow starts if you miss land drops, since experience accrual depends on lands entering
Legendary Creature — Human Warrior Ally
