If you control an untapped Archangel of Tithes, your opponents can choose to not attack with a creature that must attack if able. The same is true with respect to an attacking Archangel of Tithes and a creature that must block if able.

In a Two-Headed Giant game, if one player controls Archangel of Tithes, creatures can’t attack that player’s team or a planeswalker that player controls unless their controller pays for each of those creatures he or she controls. Creatures can attack planeswalkers controlled by that player’s teammate without having to pay this cost.