Codex of Bloodrot (Yellow)

Each hero puts a card from their hand face-down into their arsenal.

Create a Ponder token under your control and a Bloodrot Pox token under each opponent's control.

Go again

Rulings

From the Outsiders release notes

A player can’t put a card from their hand into their arsenal if they don’t have any cards in hand, or they don’t have any empty arsenal zones.
This effect is not optional. If a player has at least one card in their hand, and an empty arsenal zone, they must put a card into their arsenal.
Players choose and put one of those cards in their arsenal starting with the turn player and going in player turn order (clockwise) around the table.
Creating Ponder and Bloodrot Pox tokens is not dependent on the preceding effects.

Keyword notes

Go again - Go again allows multiple actions to be played in a turn when usually playing an action with use up your action point, and therefore end your turn. A card with go again gives the controller of that card or activated ability 1 action point when it resolves.

When an action with go again resolves, its controller gains 1 action point.
Multiple instances of go again on the same card or activated ability do not stack. If a card or activated ability has multiple instances of go again when it resolves its controller gains 1 action point only.
If an action with go again does not resolve, its controller does not gain 1 action point.
You cannot reveal a card with no to Belittle. The card must have a value to its power that is 3 or less. (0 is a value)