Yu-Gi-Oh! Master Duel has a gem system for in-game currency.
A pack of cards cost 100 gems and they have 10 cards each. Daily missions + login nets 145 gems a day so a month will get you 4350. The shop normally sells 4950 gems for $79.99 and are unlimited to purchase. Sales sell 3500 gems for $28.99 with a hard limit of 3 purchases. Whales have to accept they are getting royally screwed if they want to whale. (insert comparison/analysis to purchasing $79.99 of real life card packs and the benefits of selling them versus just under 500 random virtual cards) Sale has only been available twice since release (celebrating game release was used for both sale reasons) so I'm guessing it will be a every 3 month thing.
The way odds work when opening packs you are encouraged to open 10 at a time (1K gem cost) as a Super Rare (SR) card is guaranteed. If an Ultra Rare (UR) card wasn't obtained when opening a 10 pack then the next 10 pack is guaranteed to have 1.
Master Duel has a limited pack pool to open from.
You will need to open the Master Pack (a card pool of 6870 total) to have the opportunity to "unlock" one of the other 100 card packs (~50 card pool each) for 24 hours by pulling a SR or UR associated with the pack. So if you want to play a specific archetype you will need to save up gems (10K limit) and open a pack a day in hope you pull one of the ~15 cards associated with unlocking the card pack for them and then dumping your saved gems in hopes you pull the necessary cards to make a decent deck. This method robs you of the guaranteed benefits of opening 10 packs at a time while fishing for the pack.
Your only other alternative to this is to craft one of the ~15 cards associated with unlocking the card pack. Master Duel will unlock the card pack for 24 hours and give you a free pack as well. This craft method is limited to a one time thing per account, per pack. Collecting cards or even alternate conditions (glossy/royal finish) isn't a thing in Master Duel. You craft/play meta or enjoy losing past Gold rank. You data mine, analyze the new additions and save/spend gems accordingly.
Casual play doesn't exist unless you count solo mode versus the CPU.
This limitation on pack availability results in pushing many players into using their gems on the selection packs that are available to open for 60 days.
Running into a player playing cards that aren't from the selection packs is fairly rare.
This time its much worse as Destiny HERO - Destroyer Phoenix Enforcer got introduced in the latest selection pack Refined Blade which has resulted in several threads on the steam forums requesting a ban as the card is able to be fusion summoned using materials from the deck easily. Without negates or banishes the card runs rampant destroying 1 card on the opponents field and reviving itself each turn.
With a +10K card pool, Master Duel released to millions capable of matching players across the world to play a child's card game translated in several languages. Shit can be considered a historic event for card games but I wouldn't recommend it to anyone unless you enjoy being negated