If Do-It-Yourself Seraph has the text box of another card, it has all the abilities and flavor text of that card.

If Do-It-Yourself Seraph leaves the battlefield, it loses any text boxes it gained. If it returns to the battlefield, it will be a new object and won't have those text boxes, either.

If Do-It-Yourself Seraph has abilities that contradict one another, the most recently added one wins. For example, if Do-It-Yourself Seraph has the text boxes of both Beast of Burden (power and toughness equal to the number of creatures on the battlefield) and Psychosis Crawler (power and toughness equal to the number of cards in your hand). Do-It-Yourself Seraph's power and toughness would be defined by the text box added most recently.

If anything cares about the text of Do-It-Yourself Seraph, consider all of its text boxes as if they were one.