No, that does not work the way you want it to, for a few reasons.

First, “target” is a word with specific meaning in Magic, and in particular, Mirrorwing Dragon is referring to cards that actually say the word “target” in their text. Burn Down the House affects all creatures, but it does not “target all creatures”, because it does not use the word “target” in the text of that effect.

Second, Mirrorwing Dragon triggers when a player casts a spell. If you initially cast a spell that does not only target Mirrorwing Dragon, and then change its target to Mirrorwing Dragon, that will not trigger Mirrorwing Dragon’s ability anyway.

Third, there are actually existing mass damage spells that target a single creature, such as Chandra’s Ignition, but this will actually create a different problem. If you cast Chandra’s Ignition targeting Mirrorwing Dragon, it will create another copy of the spell targeting each other creature you control. Those copies and the original will resolve one at a time, and with all the damage being dealt, creatures can die before the copy targeting them resolves. If that happens, the spell will have no legal targets, and it will fail to resolve, and not deal any damage. It would be difficult to deal enough damage this way to kill your opponent’s creatures without already having large creatures of your own.