Unswerving Sloth

Saddle is a keyword built around a tension: you tap your team to power up the Mount, so the crew that pays the cost sits out the combat it enabled. This one refuses that trade. The untap-all clause returns every creature you tapped to saddle it, plus anything else you had committed, meaning the crew is freed up the moment the attack lands. In practice the sequence is: tap four power worth of creatures before combat, swing with an indestructible 5/5, then, once attackers are declared, untap the whole board so the saddling creatures are available to block. It collapses the usual Saddle drawback into an upside, turning a mechanic designed to force a decision (attack big, or hold back to defend) into one that lets you do both in the same turn. The indestructible rider is the part that makes the untap matter: the Mount walks through any block and most damage-based removal aimed at it during combat, so the saddling creatures aren't insulating a fragile threat, they're fueling one that cannot be killed while it's swinging, then stepping back to guard the ground behind it. It reads as a payoff for a wide board, but the structural point is subtler than that: it is the Saddle enabler that answers the keyword's own design cost, which is why it wants a crew of small attackers around it rather than a slower, single-threat shell.