@bpolitteA question about the Opal of the Ild Rune. Does the combustion property require an attack roll? nope

— Mike Mearls (@mikemearls) October 6, 2015

@bpolitte @JuanMTejadaHI asked because the other runes’ similar powers all required saves (but they also do better damage).
it requires no save – idea is that fire is undeniable, also requires touch

— Mike Mearls (@mikemearls) October 10, 2015

@JuanMTejadaH @bpolitteBut its combustion just an action or an special attack action (For example: How will it work with Sanctuary?) i'd consider it a hostile act for purposes of the spell, not technically an attack but requires a save

— Mike Mearls (@mikemearls) October 10, 2015