Cheapest priced copy (March of the Machine): $2.29 at Card Kingdom, near mint, their price list as of .
Rona, Herald of Invasion // Rona, Tolarian Obliterator 
Legendary Creature — Human Wizard // Legendary Creature — Phyrexian Wizard · 1/3 · Rare · March of the Machine · #295
Whenever you cast a legendary spell, untap Rona.
{T}: Draw a card, then discard a card.
{5}{B/P}: Transform Rona. Activate only as a sorcery. ({B/P} can be paid with either {B} or 2 life.)
Trample
Whenever a source deals damage to Rona, that source's controller exiles a card from their hand at random. If it's a land card, you may put it onto the battlefield under your control. Otherwise, you may cast it without paying its mana cost.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $2.29 to $5.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| March of the Machine | 75 | Rare | $2.49 | $3.49 |
| March of the Machine | 295 | Rare | $2.29 | $3.49 |
| March of the Machine Promos | 75s | Rare | — | $5.99 |
5 rulings from Wizards of the Coast
- 14 April 2023The spell you cast from exile without paying its mana cost is cast during the resolution of the triggered ability. Timing restrictions of that spell based on card type are ignored.
- 14 April 2023The first ability of Rona, Herald of Invasion will resolve before the spell that caused it to trigger.
- 14 April 2023Playing a legendary land won’t cause the first ability to trigger.
- 14 April 2023If the spell has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
- 14 April 2023If you cast a spell without paying its mana cost, you can’t choose to cast it for any alternative costs. You can, however, pay any additional costs. If the spell has any mandatory additional costs, you must pay those.