This should definitely be built around, using creatures with evasion, double strike, and other good damage-enhancing abilities to mutate your commander onto
For any players worried about their stuff removed, this land represents swamps and mountains and is formidable
Alternatively, you could use a card like Goldberry, River-Daughter to move one of your Finality counters around to protect the artifacts you need the most
As a starting place, you might decide to build around one of the card games popular archetypes - themes that encapsulate cards keywords, gameplay effects and lore, such as Elemental Hero, Fire Warrior or Vampire
Playing the cards exiled with Harnfel follows the normal rules for playing those cards
Even better, this stacks so every turn not only do you increase the size of your army with Terra, but you then increase their strength with Celes