21.3 The Buyer shall pay all reasonable legal and other costs reasonably incurred by the Company or the Seller (whether or not Court proceedings shall have been issued) as a result of the Buyer's non-payment for and/or failure to collect a Lot, on a full indemnity basis, together with interest thereon at the rate specified in clause 21.1(c) from the date upon which the Buyer shall have become liable to pay costs
The reason this happens is because cards don't retain any knowledge of their past when exiled, and so default back to the untransformed state when they re-enter the battlefield.
(There were Chandra Nalaar, Chandra Ablaze, Chandra, Fire of Kaladesh, Chandra, Pyromaster, Chandra, the Firebrand, and now this one.) Chandra has been one of the most disappointing entries in the Planeswalker canon
If you want to take this deck to the next level and lean harder into the Hero Typal theme, then check out our Avengers Assemble upgrade guide