Not entirely sure, but I'm going to assume from the context that the text is a warped version of "Let's transform." Usually would've been written 変身(へんしん)しよう。
And thanks to LaC who corrected ^^; Heh. That's kind of embarrassing. I didn't see that the 'よ' was a yokuon... Question, though... My dictionary shows two entries for へんしょう. Seeing as the word is written in hiragana only, how did you (LaC) come to this conclusion among the two words? Out of curiosity, as the other also seems to make some, although less, contextual sense.
