Request
The most efficient way to get Monster Cards are via Requests. Priority should be 1) Evostones 2) Monster Cards 3) Blessings of Valor/Gold
Expedition
Not recommended to select Monster Cards. Priority should be 1) Gold, 2) Dimensional Boss, 3) Monster Card/Exp It's not recommended to use this for monster cards. The priority should be gold and dimensional bosses. However, experience will be used to increase your level late game so you can increase your gold capacity cap from other methods. I've experienced the game slow pacing around level 55, others are welcomed to add their input.
Wizard's Labyrinth
Not recommended to select Monster Cards. Priority should be 1) S Rank Hero 2) Monster Card 3) Gold 4) Prana
Shop
Monster Card Summon
Though this method grants the user ranked 2-4 monster cards, this method shouldn't be the main method of obtaining monster cards as it uses gems.
Honor Shop
1. Exclusively use it to get rank 1 monster cards. This will be used for heroes ranked 3 and 4.
Request Coin Shop
Solely used for rank 3 monster cards. Use this exclusively for heroes ranked 5 and 6.