Question: I use Emerald / Reflective Shield, so spells should be reflected; I don't undestand why firebolts or deflagrations can damage my cards. Which are situations where spells ARE reflected?
Spell damage targeting you (the player, not the creatures, not the creatures, not the player's hand) is reflected. This does not include healing with the exception of Antimatter'd creatures buffed with Shard of Wisdom. Nightmare is not reflected. Unstable Gas is reflected. Purify is reflected when used by the AI/opponent but is not reflected when used by the player (the animation shows the spell being reflected but the effect still goes through); this is a bug which causes desyncs in PvP. Spells will only reflect off of 1 reflective shield at a time (i.e. if you and your opponent have a reflective shield on the field and you use Fire Bolt on yourself, Fire Bolt will be reflected onto your opponent without being reflected by the opponent's shield). The list of Easter eggs goes on and on.
There really isn't a simple answer to this, unfortunately, as it's not very consistent with what the wording indicates should happen.