Rhonas can't attack or block unless you control another creature with power 4 or greater.
: Another target creature gets +2/+0 and gains trample until end of turn.
Rhonas is a hyper-efficient mono-green beater: a 5/5 deathtouch indestructible body for three mana that's nearly impossible to remove. Deploy fat creatures to turn Rhonas on, then use his pump ability to push damage and create lethal trampling swings. You win by going wide or tall with green ramp and stomping the table with combat damage.
Indestructible deathtouch makes Rhonas an evasive, resilient threat that trades up against anything in combat.
Extremely cheap for a 5/5, freeing mana for ramp and threats.
Repeatable pump ability gives a built-in mana sink and trample enabler.
Mono-green gives access to the best ramp in the format for explosive starts.
Can't attack or block without another 4+ power creature, so a board wipe can shut him off offensively.
Mono-green lacks interaction, card draw fixes, and answers to combo/flyers.
Vulnerable to exile, -X/-X effects, and edict removal despite indestructibility.
Pump ability targets 'another' creature, so Rhonas can't buff himself.
Steady card draw and scry to keep gas flowing in a colorless-poor color.
Add the best mono-green ramp (Sol Ring, Carpet of Flowers, mana dorks) and card advantage (Beast Whisperer, Guardian Project) to offset green's weaknesses. Include haymakers like Craterhoof Behemoth and protection like Tyvar's Stand to close games and survive wraths. Tighten the curve with cheap 4+ power enablers so Rhonas comes online turn three or four consistently.