Hello, this is an odd question that I have been unable to find an answer for.
We are playing an old school format that includes every card up to and including those released in the Apocalypse expansion. From a B/R point of view this is right before Fact or fiction got the axe.
You can find more information about the format here.
The card in question is Illusionary mask. I did a lot of digging and found one of Oscar Tan's articles which states that the mask's wording at that point in time was:
Illusionary Mask - 2
X: Put a creature card with converted mana cost X or less from your hand into play face down. If the face-down creature deals damage, is dealt damage, or becomes tapped, turn it face up. Play this ability only any time you could play a sorcery.
This leaves a bit to be desired, to say the least.
If I cast swords to plowshares on the facedown creature does my opponent gain life and how much?
What is the size of the facedown creature?
If that creature is say, a Birds of paradise, can I tap it for mana while it is face down?
I also attempted to find Stephen Menendian's starcitygames article on Tainted Mask, but it seems to have disappeared into the void. As a side note in case he reads this, his article on GAT is also gone (How to clip a lotus and grow a tog)
Crystal keep is somewhat online again. Here are some notes:
This card allows you to put a creature card into play without playing it and while ignoring the colored mana requirements in its cost. [D'Angelo 2001/08/15]
The creature is considered to be a 0/1 colorless creature with no name, creature type, expansion symbol, or abilities, and a mana cost of 0. None of the true characteristics of the card apply. This is true as long as it is face down. [CompRules 2001/07/23 - 504.2]
The creature enters play face down, so none of its "comes into play" abilities will trigger or have any effect. [CompRules 2001/07/23 - 504.2]
The controller may turn it face up any time that player has priority. This action does not go on the stack. [CompRules 2001/07/23 - 504.3]
When turned face up, the creature regains its full characteristics. [CompRules 2001/07/23 - 504.4]
The creature's "comes into play" abilities (and any other abilities relating to the creature coming into play) do not trigger when it turns face up. [CompRules 2001/07/23]