Text (DK+errata): {Tap}: Untap target attacking creature. Prevent all combat damage that would be dealt to and dealt by that creature this turn. [Oracle 1999/09/03]
The creature is still part of the combat. It just has its damage prevented. Don't infer something from the fact that it becomes untapped. [D'Angelo 1999/08/01]
Can target a non-tapped attacking creature such as the Serra Angel. Both parts of the effect will happen even if one part does nothing useful. So if it untaps an already untapped card, it will still make the creature neither deal nor receive damage. [D'Angelo 1999/08/01]
Vintage tournaments (see Rule 911) restricted this card from 1994/10/10 until 1999/04/01.
Legacy tournaments (see Rule 912) banned this card until 1999/04/01.
Extended tournaments (see Rule 913) have always banned this card.
Standard (Type 2) tournaments (see Rule 914) have banned this card since 1995/06/08 since it is no longer in the environment. It was previously restricted from 1994/10/10 until 1995/06/08.
