Blades is every creature type, but is also an instant. Does Wirewood Savage's ability trigger?
If it doesn't, why is it usefull to have changeling ability on an Instant ?
Savage does not trigger since instants and sorceries do not enter the battlefield.
Changeling on an instant or sorcery is useful for a number of things. Goblin Warchief will reduce its cost (since it is a goblin spell) or you can get it back to your hand with something like Boggart Birth Rite
Let's say I have a Wirewood Savage on the battlefield and I play Blades of Velis Vel.
Blades is every creature type, but is also an instant. Does Wirewood Savage's ability trigger?
If it doesn't, why is it usefull to have changeling ability on an Instant ?
Changeling on an instant or sorcery is useful for a number of things. Goblin Warchief will reduce its cost (since it is a goblin spell) or you can get it back to your hand with something like Boggart Birth Rite