If Sun Disc is activated and then The Harrowing is played (which plays units from the graveyard), can Sun Disc be activated between the units being played so they enter ready?

Ruling: Sun Disc can only be activated at base speed when there is no chain present. Once The Harrowing begins resolving and playing units, there is no opportunity to activate Sun Disc between those units because a chain is present the entire time until all units resolve.

Sequence:

• Activate Sun Disc before playing The Harrowing
• The next unit played (whether from hand or from The Harrowing) will enter ready
• All subsequent units from The Harrowing will enter exhausted
• No activation window exists between units being played by The Harrowing

Nuances:

• If you have 2 Sun Discs active, only the first unit played will benefit from both effects (both see the same "next unit"), so it's better to activate one Sun Disc before each unit you want to enter ready
• Units in Riftbound instantly resolve when finalized to the chain, leaving no window to react even if Sun Disc were reaction speed
• When an effect instructs you to play a card, you play it when that effect is resolving and at no other time