Evasion ability

An evasion ability is a kind of static ability of a creature that improves its chances of damaging the defending player by restricting which creatures can block it. The ultimate example is "This creature is unblockable" (e.g. Tidal Kraken), but there are several other evasion abilities:

• Flying (Can only be blocked by other creatures with flying or reach) e.g. Wild Griffin.
• Fear (Can only be blocked by Black or Artifact creatures) e.g. Gluttonous Zombie.
• Intimidate (Can only be blocked by artifact creatures and/or creatures that share a color with it) e.g. Bladetusk Boar.
• Horsemanship (Can only be blocked by other creatures with Horsemanship) e.g. Lu Bu, Master-at-Arms
• Skulk (Can only be blocked by creatures with equal or lesser power) e.g. Furtive Homunculus
• Shadow (Can only block or be blocked by other creatures with Shadow) e.g. Soltari Priest.
• Menace (Can only block or be blocked by two or more creatures) e.g. Boggart Brute
• Landwalk (Is completely unblockable if defending player controls a land with this property.) e.g. Rushwood Dryad.
• Specific 'Cannot be blocked by' clauses. e.g. Sacred Knight, Vindictive Mob.
• Protection technically not, but also functions much like an evasion ability. (Cannot be blocked by creatures with this quality) e.g. Paladin en-Vec.

Some abilities act as pseudo-evasion abilities, not affecting how creatures block but instead affecting how combat damage can be assigned.

• Banding (Defending player chooses how the creature blocked by the creature(s) with Banding assigns combat damage) e.g. Benalish Hero.
• Trample (Allows excess combat damage to be dealt to the defending player) e.g. Force of Nature.
• Specific damage reassignment. e.g. Nomads en-Kor (en-Kor ability), Thorn Elemental (Super trample), Farrel's Zealot (Untrample), Laccolith Whelp (Laccoliths).

Rules

From the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

• 509.1b The defending player checks each creature they control to see whether it’s affected by any restrictions (effects that say a creature can’t block, or that it can’t block unless some condition is met). If any restrictions are being disobeyed, the declaration of blockers is illegal.
  A restriction may be created by an evasion ability (a static ability an attacking creature has that restricts what can block it). If an attacking creature gains or loses an evasion ability after a legal block has been declared, it doesn’t affect that block. Different evasion abilities are cumulative.

  Example: An attacking creature with flying and shadow can’t be blocked by a creature with flying but without shadow.