You can ‘combo’ transition classes only when they use different properties.
for example, with this markup:
<div class="slide-down slide-right fade"></div>
and these styles:
.slide-down:hover { -webkit-transform: translateY(100% ); }
.slide-right:hover { -webkit-transform: rotateX(180deg); }
.fade:hover { opacity: 0; }
When you hover over this element, it will spin upside-down and fade to zero opacity, but it will not move along its Y-axis.