IMO, should reflect harmful spells. This includes Poison, Silence, Nightmare, etc.
As it stands now, it is very situational and barely used at all. SoW was a very small buff to this card, and not enough for it to see any real playtime.
My point, exactly. After all, all these shields block is Ice Bolt and Fire Bolt. Blocking the Poison spell would, IMO, be automatically balanced by also blocking Purify. Also, Life and Light should both, as far as I know, have ways of protecting quanta from BH. After all, Sanctuary is a thing - but a single slow counter to a widely-abused spell is hardly enough. Abusing SoW requires at least a 3-card combo (quint, SoW, Mirror Shield, or Anubis, SoW, and SoR or Aether Pillars with MS), so there`s little to no danger of that becoming OP.
The only possible downside would be SoSe players reflecting poison at themselves and reflecting Purify away. And that requires using a valuable card slot for MS to block Purify, and the opponent providing one to bounce poison - not too likely a scenario.
Please, anyone who can, buff these cards!
edit: Nightmare targets a creature, not a player, and so should not be blocked. Sanctuary needs to keep its special place in blocking hand manipulation.