Sanctum PSA: Twitch drops will, by themselves, give you enough Charms to buy 2 of the new cards without even playing a single match

Twitch drops are currently active

For the 4 hour reward you're given 400 Charms and for the 6 hour reward you're given 600 Charms

The Twitch drop Charms progress your rank in the event and are enough to unlock the first 3 tiers which gives another combined 1500 Charms

That is 2500 Charms aka 2 of the new cards for free without even interacting with the game mode

If you want to push for the 3rd new card its only 350 Charms you need to earn through actually playing matches since the 4th rank (which you are only 110 Charms away from after the Twitch drops) gives another 750 Charms