are you sure about creatures transforming not entering the battlefield?

[Levi]

you say double face creatures that transform dont trigger enter the battlefield abilities?

but perhaps they do? because that creature wasnt on the battlefield before but now it is?

for example
Bloodline Keeper turns into Lord of Lineage

before: bloodline keeper on the battlefield
lord of lineage not on the battlefield

after: lord of lineage on the battlefield
bloodline keeper not on the battlefield

so shouldnt lord of lineage trigger enter the battlefield ability?

[Arix]

No, I am 100% absolutely sure.The card's characteristics change, but it's still the same object. It doesn't leave the battlefield and then come back as Lord of Lineage - it just changes its name, CMC, power, toughness, abilities and whatnot. It's no different to changing a card's colour with Tidal Visionary, or Cryptoplasm copying something different during your upkeep.

[Jake1991]

It doesn't enter the battlefield because it's already on the battlefield. It just changes it characteristics.

When a Double-Sided creature transformes, it becomes the other side of the card. Its the same as a flip card flipping and a face-down creature turning face up.