Star Athlete

You don't have to attack with the creature with blitz unless another ability says you do.

If the target permanent is an illegal target as Star Athlete's second ability tries to resolve, it won't resolve and none of its effects will happen. No player will be dealt damage, and no permanents will be sacked . . . er, sacrificed.

If the creature was cast using its blitz ability, the triggered ability that lets its controller draw a card triggers when it dies for any reason, not just when you sacrifice it during the end step.

If a creature enters as a copy of or becomes a copy of a creature whose blitz cost was paid, the copy won't have haste, won't be sacrificed, and its controller won't draw a card when it dies.

If you pay the blitz cost to cast a creature spell, that permanent will be sacrificed only if it's still on the battlefield when that triggered ability resolves. If it dies or goes to another zone before then, it will stay where it is.

If you choose to pay the blitz cost rather than the mana cost, you're still casting the spell. It goes on the stack and can be responded to and countered. You can cast a creature spell for its blitz cost only if you could cast that creature spell. Most of the time, this means during your main phase when the stack is empty.