Name:Secret Arcade
ManaCost:4 W
Types:Enchantment Room
S:Mode$ Continuous | Affected$ Permanent.nonLand+YouCtrl | AffectedZone$ Battlefield,Stack | AddType$ Enchantment | Description$ Nonland permanents you control and permanent spells you control are enchantments in addition to their other types.
AlternateMode:Split
Oracle:(You may cast either half. That door unlocks on the battlefield. As a sorcery, you may pay the mana cost of a locked door to unlock it.)\nNonland permanents you control and permanent spells you control are enchantments in addition to their other types.

ALTERNATE

Name:Dusty Parlor
ManaCost:2 W
Types:Enchantment Room
T:Mode$ SpellCast | ValidCard$ Enchantment | ValidActivatingPlayer$ You | Execute$ TrigPutCounter | TriggerZones$ Battlefield | TriggerDescription$ Whenever you cast an enchantment spell, put a number of +1/+1 counters equal to that spell's mana value on up to one target creature.
SVar:TrigPutCounter:DB$ PutCounter | ValidTgts$ Creature | TgtPrompt$ Select up to one target creature | TargetMin$ 0 | TargetMax$ 1 | CounterType$ P1P1 | CounterNum$ X
SVar:X:TriggeredStackInstance$CardManaCostLKI
Oracle:(You may cast either half. That door unlocks on the battlefield. As a sorcery, you may pay the mana cost of a locked door to unlock it.)\nWhenever you cast an enchantment spell, put a number of +1/+1 counters equal to that spell's mana value on up to one target creature.