Once their defense is depleted, they pop, go back to you, and get recast as their transformed backside for a second big bonus
Tinker doesnt even need a second card to be absurd, although frequently it was combined with Time Walk to great effect since all you need to do is untap
They used to be, sure, but in recent days, there have been plenty of changes made that affect either recently introduced mechanics like the companions, but there have also been changes to things that have been around far longer, such as cascade
3) The powerful colorless matters cards are clunky but powerful, like Kozilek, the Great Distortion, and the decks that cast them are activating Blighted Woodland or casting Explosive Vegetation to find Wastes