Board Thread:Questions and Answers/@comment-6565814-20130307112813/@comment-5706972-20130307173651

Both ways work.

The easiest/best way is evolve 10 together to get the UR version that can be enhanced (and enhance it). Now evolve 10 more together and enhance that one. Finally evolve the two enhanced cards. Total cards required: 20

The card page for (Petal) Forest Eminence Sylvain shows each version:

4888(11card) - by just evolving the base card 11 times

5251(20card) - by evolving as stated above (10 together and 10 together, then those two together)

5276(1024card) - by evolving each card at each level so that only like-level cards are ever evolved together

Note that the 20-card version is only 25 atk less than the 1024-card version. The 1024- card is not much of an increase given the number of cards required.