Can Yordle Explorer draw for Akshan if you play the additional cost?
No, Yordle Explorer will not trigger when you play Akshan, Mischievous.
Reasoning
According to the official rules and FAQs (specifically RiftJudge FAQ 8453, 8812, and 18):
- Yordle Explorer checks the printed Power cost of the card being played.
- The printed Power cost is defined as the set of Power symbols ([A]) listed in the upper left corner of the card's cost box.
- Additional costs, such as the [C][C] optional additional cost for Akshan, Mischievous, are not part of the printed Power cost and are not factored into the trigger check.
- Yordle Explorer triggers when you play a card with a printed Power cost of [A][A] or more.
Because Akshan, Mischievous has no printed Power cost symbols ([A]), he does not meet the condition to trigger Yordle Explorer, regardless of whether you choose to pay his optional additional [C][C] cost.
Note: I could not fully verify this ruling against the retrieved rules.