Shadow Sliver — ruling 1

Once a creature has been blocked, that creature remains blocked and will deal and be dealt combat damage even if it gains or loses shadow or if the blocking creature gains or loses shadow.

Shadow Sliver — ruling 2

If an attacking creature has multiple evasion abilities, such as shadow and flying, a creature can block it only if that creature satisfies all of the appropriate evasion abilities.

Shadow Sliver — ruling 3

Multiple instances of shadow on the same creature are redundant.

Shadow Sliver — ruling 4

Abilities that Slivers grant, as well as power/toughness boosts, are cumulative. However, for some abilities, like flying, having more than one instance of the ability doesn’t provide any additional benefit.

Shadow Sliver — ruling 5

If the creature type of a Sliver changes so it’s no longer a Sliver, it will no longer be affected by its own ability. Its ability will continue to affect other Sliver creatures.

Shadow Sliver : règles, fonctionnement et interactions (MTG)

Shadow Sliver is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

All Sliver creatures have shadow. (They can block or be blocked by only creatures with shadow.)

How it works : Shadow Sliver

Original English text — Wizards of the Coast / Scryfall

#1March 19, 2021· Wizards of the Coast
Once a creature has been blocked, that creature remains blocked and will deal and be dealt combat damage even if it gains or loses shadow or if the blocking creature gains or loses shadow.
No other card is named in this ruling.
#2March 19, 2021· Wizards of the Coast
If an attacking creature has multiple evasion abilities, such as shadow and flying, a creature can block it only if that creature satisfies all of the appropriate evasion abilities.
No other card is named in this ruling.
#3March 19, 2021· Wizards of the Coast
Multiple instances of shadow on the same creature are redundant.
No other card is named in this ruling.
#4July 1, 2013· Wizards of the Coast
Abilities that Slivers grant, as well as power/toughness boosts, are cumulative. However, for some abilities, like flying, having more than one instance of the ability doesn’t provide any additional benefit.
No other card is named in this ruling.
#5July 1, 2013· Wizards of the Coast
If the creature type of a Sliver changes so it’s no longer a Sliver, it will no longer be affected by its own ability. Its ability will continue to affect other Sliver creatures.
No other card is named in this ruling.