Impetuous Sunchaser

The must-attack clause is the price tag on the rate. A 1/1 flier with haste for two mana is a perfectly ordinary aggressive curve-filler; what the design adds, and what shaves a little off the cost, is the surrender of timing. The controller never decides when this creature commits to combat: it goes every turn it can, no exceptions. On an empty board or against a grounded defense, that costs nothing, since a one-power flier is happy to chip in at open air and the haste front-loads the clock the moment it lands. The friction arrives later. Once the opponent has a flier, a reach creature, or a profitable air-block lined up, the compulsion becomes a liability the controller cannot opt out of, and a savvy opponent can manufacture the trade knowing the creature has no choice but to walk into it. Effects that punish attackers (damage to attacking creatures, tap-down-then-strike removal, anything that triggers on the swing) read the must-attack line as a free invitation. It is risk-priced aggression in its cleanest form: cast it early, start dealing damage immediately, and accept that the haste is the upside while the lost agency is the cost, payable only once the board stops being empty.