This shard is good, but it is very situational. It will be more interesting when we change text into: "Target creature now deals spell damage. If Immaterial gain +4/0"
Yes. Or if not immaterial gain -4|+0.
Btw. Should it work with borrowed creatures? and with Seraph (Seraph is not immaterial it is shielded)?
Aether has got low attack, so I prefer +4/0 for Immaterial. Burrow creatures shouldn't get this bonus, because this Shard should be for Aether, but we can discuss about it.
I think also about other buff. Maybe text "Target creature now deals spell damage. If Immaterial create Lighting" will be more interesting? But I don't know what change will be better - Lighting to hand or +5 damage instantly. This card has got potential, but we must allow use it on all creatures, not only Immaterial.
And last thing. When SoW can avoid shield then also SoFr need buff. Both cards have got similar effect (avoid shield and attack bonus). +4/0 means often more than +50% critical hit and You always avoid shield. In SoFr You need seven creatures (7x15% = 105%) to get this effect every turn (statistical), SoFr is too random effect, it is easier destroy SoFr than Immaterial creature and SoFr cost much more... We need balance here (nerf SoW or buff SoFr).