No. Mimeoplasm/Impostor has an activated ability that is linked with its second (static) ability. Thornling wasn't exiled with the Mimeoplasm/Impostor's first ability, so it doesn't apply for the second ability.
Quote from CR »
607.2a If an object has an activated or triggered ability printed on it that instructs a player to exile one or more cards and an ability printed on it that refers either to "the exiled cards" or to cards "exiled with [this object]," these abilities are linked. The second ability refers only to cards in the exile zone that were put there as a result of an instruction to exile them in the first ability.
It's really unfortunate that it's worded in such a confusing way. Because the wording as written on the card implies that since it was exiled by the Mimeoplasm, it had those activated abilities. The card really should say "all creature cards exiled with its first ability"
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