Type and P/T setting effects made easy

As seen in my previous blog post, effects that set or change the types and power/toughness of a permanent can sometimes cause confusing situations. Here are some rules of thumb that can be used to make understanding these situations easier.

1. If an effect says "is/becomes a (type)" (with no "in addition to its other types"), all of that permanent's types are replaced with the new one. (For example, if it was a "Land Creature" and the effect says that it "becomes a creature", then it would lose the Land type.) All of the subtypes are likewise replaced by this.
2. If an effect only sets a subtype with "is/becomes a (subtype)" without mentioning a type (and without any "in addition to its other types") then only the subtypes of that particular category are replaced with the new subtype. (For example, if the type of the permanent was "Land Creature - Forest Dryad" and an effect says that it "becomes a Treefolk", then the type becomes "Land Creature - Forest Treefolk.")
3. If the effect in question says "in addition to its other types" or "is still a X" then it retains all of its previous types (completely regardless of what that X is.) The latter expression means the exact same thing as the former one. Also, the latter expression never adds any type to the permanent, even if it might sound so. (For example, "it's still a land" does not add the Land type to the permanent. It simply means that it retains all of its existing types.)
4. There's a specific exception to the first rule above. If an effect says that a permanent "becomes an artifact creature", then it retains all of its existing types without that effect having to say so. (This is a special exception stated by the game rules.)
5. A copy effect replaces everything in a permanent with the contents of another card, and this happens on layer 1. Effects that set or modify the type of the permanent happen on layer 4 (and thus are applied on top of any copy effect that may have been applied.) Effects that set or modify the power/toughness of a permanent happen on layer 7 (on different sublayers depending on the kind of effect.) If two effects would set or modify the same thing on the same layer or sublayer, the one with the newest timestamp wins. If two effects would get the same timestamp (eg. because they are entering the battlefield at the same time) the active player decides their order.

(Note that copy effects and layers are more complex than this, but those details are beyond the scope of this short list.)