Rona, Herald of Invasion
Legendary Creature — Human Wizard
Whenever you cast a legendary spell, untap Rona.
: Draw a card, then discard a card.
: Transform Rona. Activate only as a sorcery. ( can be paid with either 
or 2 life.)
Rona, Tolarian Obliterator
.
Legendary Creature — Phyrexian WizardTrample
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.
Daniel Lieske
March of the Machine (MOM)
• #295Rulings
The 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.
(wotc • 2023-04-14)
The first ability of Rona, Herald of Invasion will resolve before the spell that caused it to trigger.
(wotc • 2023-04-14)
Playing a legendary land won’t cause the first ability to trigger.
(wotc • 2023-04-14)
If 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.
(wotc • 2023-04-14)
If 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.
(wotc • 2023-04-14)
Rulings
The 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.
(wotc • 2023-04-14)
The first ability of Rona, Herald of Invasion will resolve before the spell that caused it to trigger.
(wotc • 2023-04-14)
Playing a legendary land won’t cause the first ability to trigger.
(wotc • 2023-04-14)
If 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.
(wotc • 2023-04-14)
If 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.
(wotc • 2023-04-14)