Michelangelo, Improviser

Putting a land card onto the battlefield with Michelangelo's last ability doesn't count as playing a land. You can put a land card onto the battlefield this way even if you've already played a land for the turn.

Spells can only be cast for their sneak costs any time you could play an instant during the declare blockers step on your turn (after your opponent has decided whether to block).

Although a creature put onto the battlefield this way is attacking, it was never declared as an attacking creature. Abilities that trigger whenever a creature attacks won't trigger when that creature enters attacking.