Hello. In this posts (HERE and HERE) is cited&stated, that any 'duration' effects of terrain cease when terrain leaves play. There's also stated, that 'second' effect of Circle of Steel is 'duration' effect:
Circle of Steel Terrain Battle: (1) Your Personalities at this battlefield have +1F/+1C while they have an attachment. (2) After this battle resolves, until your next turn ends, your Personalities who were at this battlefield during resolution can not be targeted by other players’ actions while they have an attachment and are not in an army.
Question #1 : according to above mentioned posts, Circle of Stell effect (2) ceases to exist immediately after battle, when terrain hits discard pile. Right ? If not, please specify why... because I cannot find it myself.
Question #2 : if answer to #1 is 'no', then how's about Unshakable & Circle of Steel ?
Post that makes my head hurt : Matsu Wani : I use unshakable to play circle of steel from the discard pile. All the units I control get +1/+1 as long as they have an attachment. The unshakable leaves play taking the circle with it. Do the units now lose the +1/+1? Zen Faulknes : Yes. That's an effect with a duration, so it ends due to the terrain leaving. viewtopic.php?f=59&t=60968 Matsu Wani : Are units able to be targeted on my next turn? Zen Faulknes : Yes, because that's a delayed effect. LINK