Can Defy counter Siphon, given that Siphon costs 2 energy and 1 power?

Ruling: Yes, Defy can counter Siphon. Siphon costs 2 energy and 1 power, which meets Defy's requirement of no more than 4 energy and 1 power.

Nuances:

• Split power costs (like Siphon's blue or yellow power) still count as 1 power for the purposes of Defy's targeting restriction