Enduring Friendship is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Double team Whenever you cast an instant or sorcery spell, creatures you control that are Otters and/or enchantments get +1/+1 until end of turn. When Enduring Friendship dies, if it was a creature, return it to the battlefield under its owner's control. It's an enchantment. (It's not a creature.)