edhseer Commander synergy, explained
Instant
Mana cost: {1}{U}
Tap up to two target creatures.
on-cast —
If there are two or more instant and/or sorcery cards in your graveyard, those creatures don't untap during their controllers' next untap steps.
on-cast —
Causes: tap a creature.
Cares about: an instant in a graveyard, a sorcery in a graveyard.
an instant in a graveyard — 2 cards in the game can cause this (Send to Sleep is one).
a sorcery in a graveyard — 2 cards in the game can cause this (Send to Sleep is one).
1 other card cares about it too. These are the ones with the most connections.
a creature becomes tapped — 565 cards in the game can cause this (Send to Sleep is one).
When a creature becomes tapped thanks to Send to Sleep:
11 other cards care about it too. These are the ones with the most connections.
anything becomes tapped — 699 cards in the game can cause this (Send to Sleep is one).
1 other card cares about it too. These are the ones with the most connections.
an instant is cast — 3,931 cards in the game can cause this (Send to Sleep is one).
When Send to Sleep is cast:
427 other cards care about it too. These are the ones with the most connections.
anything is cast — 31,128 cards in the game can cause this (Send to Sleep is one).
When Send to Sleep is cast:
5 other cards care about it too. These are the ones with the most connections.