I was playing a game with a friend and this card came up. I was attackin him with 3 of my 5 creatures, the other two I had were not attacking and were going to be kept back for blocking. He then cast illusionist gambit, forcing my 3 attacking creatures to attack his fiance. I chose to send my 2 creatures who were not originally attacking at him. He stated that the second combat is only for the creatures who were attacking during the first combat where as I argued that this wasn't the case, that it does not specify that. Help?
You are correct. Illusionist's Gambit creates an additional combat phase; the only thing out of the ordinary about that combat is that the creatures affected by the Gambit are required to attack and can't attack the Gambit's caster or their planeswalkers. Other creatures are neither required to attack nor restricted in terms of who they may attack (edit: or, more to the point, whether they may do so).
If you were playing this in a two player game, could you force your opponent to attack himself?
No, creatures can't attack their controllers. In a two-player game this essentially untaps the attacking creatures and creates another combat in which the affected creatures can't attack.
You are correct. Illusionist's Gambit creates an additional combat phase; the only thing out of the ordinary about that combat is that the creatures affected by the Gambit are required to attack and can't attack the Gambit's caster or their planeswalkers. Other creatures are neither required to attack nor restricted in terms of who they may attack (edit: or, more to the point, whether they may do so).
No, creatures can't attack their controllers. In a two-player game this essentially untaps the attacking creatures and creates another combat in which the affected creatures can't attack.