Hi, thanks for looking into this. This has been ruled explicitly by FFG:
189 – I have two questions regarding Magik’s ability to play the top card of her deck as if in hand: “Once per phase, you may play the top card of your deck as if it was in your hand, reducing its resource cost by 1.” 1. Can I play her ally Colossus in the villain phase from the top of her deck using his ability “Interrupt: When an enemy attacks you, play Colossus from your hand (paying his resource cost) and declare him the defender without exhausting him.”? 2. Can I play the top card of her deck with Team-Building Exercise: “Hero Action: Exhaust Team-Building Exercise → play a card from your hand that shares a trait with your hero, reducing its resource cost by 1.”?
Yes; using Magik’s ability, you can play Colossus (AOA #31) from the top of your deck during the villain phase and trigger his Interrupt ability. Yes; while playing a card from the top of your deck as Magik, it is considered to be “in your hand” for abilities such as Team-Building Exercise. (However, the card is not considered in your hand for other purposes, such as when you need to spend a resource or discard a card “from hand.”)
(Taken from here: https://hallofheroeslcg.com/latest-ffg-rulings-post-rrg-1-5/)
Thanks in advance!