Ichthyomorphosis — ruling 1

Ichthyomorphosis may enchant a permanent that is only temporarily a creature, such as a Vehicle. If this happens, Ichthyomorphosis will be put into its owner’s graveyard as a state-based action once the creature stops being a creature.

Ichthyomorphosis — ruling 2

Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature may become lethal if Ichthyomorphosis becomes attached to it during that turn.

Ichthyomorphosis — ruling 3

If the affected creature gains an ability after Ichthyomorphosis becomes attached to it, it will keep that ability.

Ichthyomorphosis — ruling 4

Ichthyomorphosis overwrites all colors and creature types the enchanted creature has. It’s just a blue Fish. The creature keeps any supertypes (such as legendary) it has, as well as any other card types it has (such as enchantment).

Ichthyomorphosis — ruling 5

Ichthyomorphosis overwrites all previous effects that set the creature’s base power and toughness to specific values. Any power- or toughness-setting effects that start to apply after Ichthyomorphosis becomes attached to a creature will overwrite this effect.

Ichthyomorphosis — ruling 6

Effects that modify a creature’s power and/or toughness will apply to the creature no matter when they started to take effect. The same is true for any counters that change its power and/or toughness.

Ichthyomorphosis : règles, fonctionnement et interactions (MTG)

Ichthyomorphosis 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

Enchant creature Enchanted creature loses all abilities and is a blue Fish with base power and toughness 0/1.

How it works : Ichthyomorphosis

Original English text — Wizards of the Coast / Scryfall

#1January 24, 2020· Wizards of the Coast
Ichthyomorphosis may enchant a permanent that is only temporarily a creature, such as a Vehicle. If this happens, Ichthyomorphosis will be put into its owner’s graveyard as a state-based action once the creature stops being a creature.
No other card is named in this ruling.
#2January 24, 2020· Wizards of the Coast
Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a creature may become lethal if Ichthyomorphosis becomes attached to it during that turn.
No other card is named in this ruling.
#3January 24, 2020· Wizards of the Coast
If the affected creature gains an ability after Ichthyomorphosis becomes attached to it, it will keep that ability.
No other card is named in this ruling.
#4January 24, 2020· Wizards of the Coast
Ichthyomorphosis overwrites all colors and creature types the enchanted creature has. It’s just a blue Fish. The creature keeps any supertypes (such as legendary) it has, as well as any other card types it has (such as enchantment).
No other card is named in this ruling.
#5January 24, 2020· Wizards of the Coast
Ichthyomorphosis overwrites all previous effects that set the creature’s base power and toughness to specific values. Any power- or toughness-setting effects that start to apply after Ichthyomorphosis becomes attached to a creature will overwrite this effect.
No other card is named in this ruling.
#6January 24, 2020· Wizards of the Coast
Effects that modify a creature’s power and/or toughness will apply to the creature no matter when they started to take effect. The same is true for any counters that change its power and/or toughness.
No other card is named in this ruling.