CardName: Suspicious Wall
Cost:
Type: Land - Dungeon
Pow/Tgh: 3/
Rules Text: (This enters the battlefield with three quest counters.
Whenever a source you control would deal damage, you may
remove that many quest counters from this instead. When the
last is removed, transform it.)
{T}: Add {C} to your mana pool.
Flavour Text:
Back side:
CardName: Hidden Treasure Room
Cost:
Type: Land
Pow/Tgh: /
Rules Text: {T}: Add {C} to your mana pool.
{1}, {T}, Sacrifice Hidden Treasure Room: Add three mana of
any one color to your mana pool.
Flavour Text:
Set/Rarity: A Link to the Coast Common
Suspicious Wall
C
Land – Dungeon
(This enters the battlefield with three quest counters. Whenever a source you control would deal damage, you may remove that many quest counters from this instead. When the last is removed, transform it.) : Add to your mana pool.
3
Hidden Treasure Room
C
Land
: Add to your mana pool.
, , Sacrifice Hidden Treasure Room: Add three mana of any one color to your mana pool.
: Add 
to your mana pool.
,
See Suspicious Wall. See Fire Temple.
Since going through dungeons/rooms to get a reward seems to be a common theme, why not tie it into a card type with extra rules baggage?