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 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.

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.

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

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 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.