The Dragon Hunter scenario originates from a penny arcade forum.

Canopy Cover {1G} |Enchantment — Aura| Enchant creature / Enchanted creature can't be blocked except by creatures with flying or reach. / Enchanted creature can't be the target of spells or abilities your opponents control. · WWK

Woodland Changeling {1G} |Creature — Shapeshifter| 2/2 Changeling · LRW

Dragon Hunter {W} |Creature — Human Warrior| 2/1 Protection from Dragons / Dragon Hunter can block Dragons as though it had reach. · DTK

Amanda attacks with Woodland Changeling which is enchanted by Canopy Cover. Nathan controls Dragon Hunter. Can Dragon Hunter legally block Woodland Changeling?

Some thoughts on possibly relevant rules:

609.4: Some effects state that a player may do something “as though” some condition were true or a creature can do something “as though” some condition were true. This applies only to the stated effect. For purposes of that effect, treat the game exactly as if the stated condition were true. For all other purposes, treat the game normally.

509.1b: The defending player checks each creature he or she controls 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.

609.1: An effect is something that happens in the game as a result of a spell or ability. When a spell, activated ability, or triggered ability resolves, it may create one or more one-shot or continuous effects. Static abilities may create one or more continuous effects. Text itself is never an effect.

We know that Changeling is a dragon from its shapeshifter creature type. Canopy Cover requires a blocking creature to have flying or reach. The rub begins when we look at Dragon Hunter. There's two camps of judges:

1. 609.4 interpreted the “as though” Dragon Hunter's dragon blocking ability gaining reach as an effect. When blocking a dragon, the condition is true (has reach). Dragon hunter is a legal blocker against the Changling.

2. 609.4 interpreted Dragon Hunter's effect into the “for all other purposes, treat the game normally.” Dragon Hunter does not explicitly have reach, which is required by Canopy Cover, to be a legal blocker. Dragon Hunter is not a legal blocker.

Which ruling is correct and why?

Edited Erik Simonson (April 21, 2017 10:26:47 AM)

Dragon Hunter can block a Changeling enchanted with Canopy Cover for the same reason it can block a Dragon with flying: for the purposes of determining the legality of blockers when blocking a creature with the Dragon creature type, Dragon Hunter is treated as though it has reach.

The Changeling is a Dragon, and Canopy Cover doesn't stop creatures with reach from blocking it, so the block is legal.