Microtransactions in MultiVersus are summarized as...
The game features many playerable characters most of which must either be unlocked using in-game earned gold or using the premium currency. When purchased with premium currency all currently available characters add up to over $90 USD. This is with 15 purchasable characters at roughly $7 USD each. However many more characters are planned, each likely costing a similar price.
The game features 3 "deluxe" editions which reward in-game items. These rewards include exclusive cosmetics such as banners and special effects, but also premium currency bundles, battle passes, and character unlock tokens. The most expensive pack costs roughly $100 USD and includes 30 character unlock tokens, which gives an idea of how many characters they plan to release.
The game features a battle pass. The battle pass features a lot of low tier content such as stickers, consumables, effects, xp boosts, etc. It also contains a handful of skins.
The premium store is not yet fully available and is listed as "Coming soon". Despite the premium store not being available yet some characters do have skins and other cosmetics available for purchase. Skins range from 500 Premium currency to 2000 Premium currency. However there is no way to obtain 500 directly, the lowest amount is 450 and the next step up is 1000.