My French is not the best, but I think the final chapter of the saga says "choose a creature or planeswalker. Each creature with power 4 or more you control deals damage equal to its power to that permanent."
Also, is the transformation to a 4/4 permanent? Can't tell.
French speaker here, small correction to the translation in the first post
The Bears of Littjara 1GU
Enchantment - Saga
I - Create a 2/2 blue Shapeshifter creature token with changeling.
II - Any number of target Shapeshifter creatures you control are power and toughness 4/4 (-> doesn't say until EOT)
III - Choose up to one target creature or planeswalker. Each creature with 4 or more power deals damage to that permanent target equal to its power.
Mystical Reflection 1U
Choose target non-legendary creature. The next time at least one creature or planeswalker enters the battlefield this turn, they enter as a copy of the chosen creature.
Ah so its less bonkers than the initial translation.