Use "Polymerization" to Fusion Summon "Terra Firma", then use "Miracle Fusion" to Summon a second one. By Tributing one of them, you can easily boost the ATK of "Terra Firma" to 5000.
You could even use "Parallel World Fusion" on next turn to Summon a third copy and return the Materials to your Deck.
Instead of Summoning an extra copy of this card, use "Miracle Fusion" to Summon "Elemental HERO Absolute Zero" and sacrifice it. This card will still end up with 5000 ATK but the effect of "Absolute Zero" can clear the way for a direct attack.
During your draw phase, use "De-Fusion" on "Terra Firma" to get "Elemental HERO Woodsman" and "Elemental HERO Ocean" to your field. During your Standby Phase if you have a "Elemental HERO Stratos" and a "Polymerization", you can re-Summon "Stratos" to destroy your opponent's Spell and Trap Cards (or to obtain a HERO) and the fuse "Woodsman" and "Ocean" into "Terra Firma" again.
Use this card in combination with "Elemental HERO Absolute Zero". Use "Polymerization" with "Elemental HERO Ocean" and "Elemental HERO Woodsman" to get "Terra Firma" on the field. Then use "Miracle Fusion" with "Ocean" and "Woodsman" to Summon "Absolute Zero". The use the effect of "Terra Firma" and tribute "Absolute Zero". Since "Absolute Zero" has left the field, all your opponents monsters are sending to the Graveyard, giving you a free attack with "Terra Firma".
You can use this cards effect several times on the same turn e.g. Tribute 2 "Elemental HERO Clayman" and get 1600 more ATK then "De-Fusion" to inflict a possible 6600 damage in one turn.
Use this card in combination with "Hero Mask". you can take control of your opponent's monster and Tribute them after changing their name to the targeted Elemental HERO.
You can use this card's effect to send Elemental HERO Fusion Material monsters to the Graveyard and have "Terra Firma" gain ATK. Use "Miracle Fusion" on the Fusion Material monsters sent to the Graveyard by this effect. If you Special Summon "Elemental HERO Electrum", then the cards that were banished will be shuffled into the Deck instead. If you want, you can Tribute Electrum, using the effect of "Terra Firma" to have him gain ATK up to 5400.
You can use this card in combination with "Fake Hero".
If you have various "Elemental HERO" monsters in your Graveyard, you can summon Elemental HERO Escuridao and Tribute him so that Terra Firma can obtain all of Escuridao's ATK.
You can Fusion Summon Elemental HERO Gaia and use his effect of taking the half of an enemy monster's ATK and gain that same amount of ATK, then Fusion Summon Terra Firma and Tribute Gaia, which will give you a very outstanding increase in ATK.