League of Legends

League of Legends offers many microtransactions, most of which are cosmetic only, but some include gameplay altering elements.

The primary method of purchasing anything in the game is through a premium currency called "Riot Points", or "RP" for short. RP can only be purchased in set bundles where 1000 RP equals roughly 10 USD, with larger bundles granting slightly more RP relative to the cost.

Next to the premium currency the game also offers a free currency named "Blue Essence". This is earned through regular gameplay, such as leveling your character, completing certain missions, or converting other game currencies. This currency is primarily used to purchase new characters.

Playable characters

The game allows the purchase of many playable characters. These can be purchased for RP or Blue Essence. When a new champion is released they almost always cost 975 RP (or roughly 10 USD) or 7800 Blue Essence. Over time the RP and Blue Essence cost are reduced as new champions are released. For instance, after the first week the Blue Essence cost is reduced to 6300, after 2 seasons the RP cost is reduced to 880 RP (Still requiring the same 10 USD bundle purchase) and 4800 Blue Essence. This is where most champions will stay at. Some champions may be at different price points, especially those released over a decade ago. Purchasing all champions costs over 100.000 RP, or over 600 USD through the most expensive RP bundles.
It can be argued characters provide an inherent advantage. Some characters are more powerful than others and not being able to play certain characters against others may put you at a disadvantage. If you wish to play at a high level you might find value in owning as many characters as possible. This additionally incentivizes the developers to create new characters in as strong a state as possible to encourage the purchase of new characters. It's not fair to assume the developers would be doing that on purpose, if at all, but it is something to keep in mind.

Cosmetics

The game offers many cosmetic items that can be purchased with the premium currency. The most prominent of which are character skins. These range in quality and price. The lowest being roughly 750 RP (requiring the 10 USD RP bundle), and the most expensive being 3250 RP (Requiring the 35 USD RP bundle). Most skins are available at all times, but the game also offers seasonal or temporary items, as well as timed discounts. Purchasing all character skins would cost close to 10.000 USD.
There are more items available other than skins, such as emotes, ward skins, and more. All items are cosmetic only and don't provide in-game advantages.

Some cosmetics can be earned through free in-game means through "Hextech Crafting". This system allows you to spend in-game earned currencies on lootbox like systems. You can earn "Hextech Chests" through regular play (If you play well, primarily), or by purchasing Chests with RP. Chests can be opened with keys, which are earned through regular play as well, or are purchased together with the chest when purchased with RP.
Chests don't directly award cosmetics, instead they award "shards", which can be used to craft those cosmetics. The system is rather complex and obtuse. Presumably intentionally to get you to buy more chests.

Skin bundles

League of Legends recently released their new "Legend" bundles. These are bundled centered around a particularly well known pro player. The first release includes 3 bundles for one of the players.
The prices on these varies a lot.
- Risen Legend Collection; for 5.430 RP (roughly 45 USD) you earn a character skins, the character itself, and a bunch of other emotes
- Immortalized Legend Collection; for 32.430 RP (roughly 250 USD) you earn a character skin along with many many cosmetic items. Ranging from player profile customization to in-game emotes
- Signature Immortalized Collection; for 59.260 RP (roughly 450 USD) you earn many unique cosmetics that are include the pro player's signature.
These bundles are outlandishly expensive and their cost is not justified at all. These are expected to be released more frequently over time.

Battle Passes

The game offers Battle Passes that are often tied to events, rather than seasons and are less regular as a result. These function similarly to other games, expiring if you do not complete them in time. The latest battle pass "Hall of Legends Pass" costs 1,950 RP (roughly 22 USD).
Previous Battle Passes have awared tickets rather than items directly. These tickets could be used to unlock the items of your choice. If you did not spend the tickets before the event was over, you would lose all your tickets and with that lose your money.

League of Legends has always been an expensive game. The game has added many new forms of cosmetics over time, as well as increasing the cost of existing options. While it's entirely possible to play the game without ever spending money, many of the game's content releases center around cosmetics. If you do care about player expression, expect to spend money, and a lot of it.