Basically it makes REBD and BEWD immune to things like Daedalus for one turn if they're special summoned. You can also do a combo like: send face-up dimension gate to the graveyard to summon a token, bring the banished monster back then tribute both for a BEWD. Pretty darn good card.
Search for a Divine Dragon Lords deck on YouTube. You will get an idea of how to better use Felgrand Dragon along with Guardian of Felgrand and this card. Felgrand Dragon can be obtained from the dragon structure deck.
When this is on the field, summon Paladin of Felgrad to fetch a dragon, then send that dragon to the grave using Ruins to create a Token, then sac the token and paladin to summon any high level dragon from the grave.