Semi-Evo Cards are cards that are playable before their full level because they have strong stats and unlock their abilities before their final level.
In the competitive games of EFC, one of the biggest challenges is making a strong EFC deck and still meet the 25 Star Requirement. Regardless, knowing which cards are SemiEvos can help you make formidable and strong decks for EFC.
New SemiEvos: Mrs Spool, Hydra, El Bengal... (I'm probably missing more, but I'll check)
I have heard of cases where former SemiEvos are returning to become SemiEvos and also looking out for them as well.