So, the mechanic that sort of inspired this thread for complex mechanics is the astrologian's card draw mechanic.
Hailing from Final Fantasy XIV: Heavensward, Astrologians are a healer role class with a secondary mechanic which utilises randomly drawn cards to bestow buffs on their allies. The idea of it having random draws with a little ability to manipulate outcomes with a variety of effects so you have a grab-bag of useful buffs for different situations. In-game, the draw mechanics have timers and cooldowns as part of the balancing factors since buffs in general can be overpowered if not controlled. It's less a concern here given M&M's limited capabilities for buffing other player characters.
There are a total of 8 cards, 6 cards that can be drawn by the regular Draw effect and 2 special ones that can randomly be drawn by sacrificing a drawn card. The Balance, The Bole, The Arrow, The Spear, The Ewer and The Spire are the regular cards, while the Lord of Crowns and the Lady of Crowns are the two special cards drawn by Minor Arcana.
A card can be drawn every 30 seconds, and each buff lasts 30 seconds. Only one buff may be on an ally at any given time, so buffs, the same or different, do not stack, only the most recent kicks in.
These are the related effects that are used in the Astrologian's deck mechanics;
Draw: Draws one of the six regular cards from the Astrologian's deck. The card may be held for 30 seconds during which time no other card may be drawn. Once the card is used, or one of the other Draw-mechanic effects is used, Draw may not be used again for 30 seconds.
Redraw: Returns a drawn card to the deck and draws a different card from the five remaining cards. A redrawn card otherwise has the same timers and cooldown as a card drawn by the Draw effect.
Spread: Sets a card aside. This allows an astrologian to hang onto a card, removing the timer for using it and allowing them to call on the card's power at an opportune time. Unlike Redraw, spread does not prevent the same card from being drawn again later.
Royal Road: Expends a drawn (or redrawn) card to empower the next card that is used whether used from Draw or the Spread. Only a card that is being held by Draw or Redraw can be expended for Royal Road (not a card in the Spread). The card expended determines in what way the next used card is empowered.
Minor Arcana: Expends a currently drawn (or redrawn) card in order to randomly draw either the Lord of Crowns or the Lady of Crowns. Like Royal Road, the expended card cannot come from the Spread. Also, the Lord and Lady of Crowns cannot benefit from Royal Road.
Undraw: At any time, a Drawn card, a card in the spread or a royal road effect can be released. Draw and Spread cannot normally be overridden by using the effect again, the card must either be undrawn or used to free up the space. Royal Road on the other hand can be overwritten by expending another card.
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So we'll tackle each of these effects one by one, starting with the engine of this mechanical construct,
Draw.
Draw: Variable X, Free Action, Limited (Specific Constructs)(-2)*, Uncontrollable
Cost: 4pp per rank
* = Limiting Variable to a certain subset of possible powers would be a normal -1 flaw, but in this case, we're limiting to 8 specific power configurations,
so -2 per rank feels justified. If this mechanic were to be used in a modified way for a deck with more options, a GM may use discretion to drop this it -1 per rank.
The engine that makes this mechanic run. We need enough ranks in there to build the most expensive of the 8 cards, but depending on power level, it should need too many ranks overall. Draw is set to allow a free action be used to draw a card from one of the six regular cards, allowing the standard action to remain to use the card some time before the next card is drawn. Uncontrollable is the workhorse here really. It's not so uncontrollable as in it works randomly or without the player's desire to do so, but it IS uncontrollable in that it follows certain rules; The card being drawn is randomly decided by the GM, once the card is used, sent to the spread or expended for Minor Arcana or Royal Road, the power cannot be used again for 5 rounds, and if the card is not used within 5 rounds, the variable automatically resets and may not be used for 5 rounds following.
This basically makes it function like in the game, with Uncontrollable making up for some rules that simply don't exist as flaws or mechanics in M&M.
Redraw: Feature 2 (Draw a different card once per draw, Reset Drawn card timer)
Cost: 2pp
This is pretty straight forward. It allows the player to replace the card they got with Draw with one of the other five normal cards drawn at random. This can be done at any time the Drawn card is being held and resets the 5 round limit imposed by Uncontrollable. Redraw does two things, so it's worth two Feature ranks. It can only be used one time when a card is drawn. The next time Draw is used, Redraw can be used once more. In essence, it shares a cooldown with Draw.
Spread: Feature 1 (Save a card until used), Quirk (Once used, Spread is unavailable for 5 rounds)
Cost: 1pp
Again, fairly straight forward. Once a card is drawn, the player may use Spread at any time using the 5 rounds they may hold the card, to expend it and place the card in the spread. This Feature explicitly allows the player to bypass the Variable's uncontrolled flaw and set it to a specific configuration, but only once. It does allow them to hold a card for specific timing, and doesn't interfere with them drawing other cards later on. Unlike with Redraw, having a card in the Spread does not prevent another copy of it from being drawn.
Minor Arcana: Feature 1 (Expend a drawn card to randomly draw the Lord of Crowns or Lady of Crowns and save the card until used)
Cost: 1pp
This Feature basically just opens access to Lord and Lady of Crowns, however, it works more like Spread. The Lord and Lady card expends the drawn card, starting the 5 round cooldown imposed by uncontrolled for Draw, but like Spread, Minor Arcana is an explicit exception to Uncontrolled, allowing the player to hang onto either the Lord or Lady until they need it. A player is thus able to have a Drawn Card, and Spread Card and a Minor Arcana card all at one time.
Royal Road: Array, 3 effects
Empowered: Variable X, Free action, Limited to Enhancing Card effect rank, Quirk(Can only use this array slot if a Balance or Bole card is expended)
Extended: Feature 1 (A card effect may be sustained for 10 rounds), Quirk(Can only use this array slot if an Arrow or Spear card is expended)
Expanded: Enhanced Power, Area (Burst), Selective, Variable Descriptor 2(Any normal card effect), Quirk(Can only use this array slot if an Ewer or Spire card is expended)
Cost: <Empowered> 6pp per rank -1pp, <Extended> 1pp, <Expanded> 2pp per rank +1pp
Royal Road is an interesting power array as each slot works completely differently with vastly different costs. Empowered is self contained, simply adding ranks to the existing card and probably only needs 1 or 2 ranks making that 6pp/rank cost not so scary, Extended simply modifies Uncontrolled on the Draw variable slightly, changing the time a power may be maintained for, and Expanded requires enough ranks in it to cover the ranks of the card effects (probably somewhere between 4 and 6). All three array slots have a quirk that does not allow the slot to be used until a drawn card is expended. The card in the Spread cannot be used for Royal Road. That said, the Royal Road will remain in effect until a card, either drawn or from the spread, is actually used. It is also not said in the write up, but the slot can only be used ONCE when a drawn card is expended to set the array.
Worth noting, I'd mark Final Fantasy XIV around PL6 or 7, so the card effects, as buffs, would be around there if not a little lower in rank.
Undraw: Feature 1 (Allows a drawn or spread card or the royal road to be undrawn)
This feature technically does three things, however, they are all in essence the same thing. For the drawn or spread card, it simply erases the configuration that was active or saved. For Royal Road, it effectively "uses" it so it is empty. While the Royal Road being empty is normally not an issue, it CAN be for Sleeve Draw (See below).
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Now, I mentioned an ability called Sleeve Draw before. In game what it does it randomly sets a card in Drawn, Spread, Royal Road AND Minor Arcana with Redraw as an option available to switch the Drawn card. Each effect is random but all done at once, and it's entirely possible with M&M and this mechanical construct here, and while I think I would normally save it for a stunt, this is how I would build it either way.
Sleeve Draw: Feature 4 (Randomly draws for a Drawn card, a Spread card, Royal Road and Minor Arcana), Quirk (Will not affect any cards already in play)
Cost: 3pp
I gave it 4 points of Feature simply to set the card configuration for Draw, Spread and Minor Arcana and randomly selects a Royal Road array slot as if an appropriate card were expended. The quirk is there as this does not have any Redraw effects on anything, so if the player had Lord of Crowns in their Minor Arcana, it would not be randomly chosen again, it would remain as is. If Royal Road is not empty, then it will not be changed by Sleeve Draw. The reason it is a quirk is specifically because it won't allow you to use the power as a sort of global Redraw.
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And that is more or less it for the deck mechanics. I may end up doing the cards as well, though they are a little trickier due to how finnicky M&M can be with buff-oriented powers.
To modify it for use with your own character and their own deck; the more basic thing would be using the Draw and Undraw power by themselve and possibly even Minor Arcana if they have a set of specific more powerful cards. Redraw, Spread and Royal Road are more specific to replicate the mechanics found in-game, but are largely unnecessary to a character that can simply draw random cards that have various effects.
Uncontrolled on Draw can also be negotiated with the GM as to the cooldown times, if it should even have one at all. Mileage may vary by game, but overall, the mechanic can work well for a card-using character that likes to try their luck with random outcomes.