Hi there Splinterbros and Splintersis!
In this post, I will be teaching you on how to send multiple cards in just one transaction. This will be helpful if you are on the Buy and Sell side of the game, or just gifting different cards without torturing yourself in the hassle way of sending them using the in-game method.
For this tutorial, we need to go to https://peakmonsters.com/ and login your account. Once logged in, click the My Cards section on the upper left screen.
Once there, hover your mouse or scroll down on the right side until you see the selection with Owned. Make sure that you check YES (See highlighted)
After that, select the cards that you will be sending by clicking the empty box on the left side. If you are sending all of your cards at one go, just click the 
Once you've selected the cards that you will be sending, look at the upper right side of the screen and click this logo: 
Select Transfer, then type in the IGN of the player that you will sending the cards to. Make sure that there is a green check beside the IGN. This means that you've typed the IGN correctly.
By the way, it is case sensitive so make sure that you've typed and checked before clicking Confirm.
Finally, approve the transaction via Keychain. And there you go. Instead of sending the cards individually in-game, you just saved a ton of time and effort by sending them via Peakmonster.
Hope that this will help especially the newbs and even the vets that are not aware of this feature.
PS.
*I was away in splintertalk for quite a while. I was Positive from Covid some time ago and I just fully recovered recently. Yeah, it has been a challenge especially the quarantine part.
Sharing this to spread awareness and to remind you guys to always be safe out there. Wear your masks!
Anyways, wishing you guys good health and prosperous END OF SEASON REWARDS! We will beat this virus very soon. Sending love! <3*