Lovestruck Beast // Heart's Desire — ruling 1

You don't have to attack with a 1/1 creature for Lovestruck Beast to be able to attack. You just need to control a 1/1 creature.

Lovestruck Beast // Heart's Desire — ruling 2

Once Lovestruck Beast is attacking, it'll remain attacking even if you no longer control a 1/1 creature.

Lovestruck Beast // Heart's Desire — ruling 3

If Lovestruck Beast's power and toughness are reduced to 1/1, it learns that loving oneself is the first step on the true path to happiness, and it can attack even if you control no other 1/1 creatures.

Lovestruck Beast // Heart's Desire — ruling 4

An adventurer card is a permanent card in every zone except the stack, as well as while on the stack if not cast as an Adventure. Ignore its alternative characteristics in those cases. For example, while it's in your graveyard, Giant Killer is a white creature card whose mana value is 1. It can't be the target of the triggered ability of Mystic Sanctuary.

Lovestruck Beast // Heart's Desire — ruling 5

When casting a spell as an Adventure, use the alternative characteristics and ignore all of the card's normal characteristics. The spell's color, mana cost, mana value, and so on are determined by only those alternative characteristics. If the spell leaves the stack, it immediately resumes using its normal characteristics.

Lovestruck Beast // Heart's Desire — ruling 6

If you cast an adventurer card as an Adventure, use only its alternative characteristics to determine whether it's legal to cast that spell. For example, if Giant Killer is exiled with the last ability of Vivien, Champion of the Wilds, you can't cast it as Chop Down.

Lovestruck Beast // Heart's Desire — ruling 7

If a spell is cast as an Adventure, its controller exiles it instead of putting it into its owner's graveyard as it resolves. For as long as it remains exiled, that player may cast it as a permanent spell. If an Adventure spell leaves the stack in any way other than resolving (most likely by being countered or by failing to resolve because its targets have all become illegal), that card won't be exiled and the spell's controller won't be able to cast it as a permanent later.

Lovestruck Beast // Heart's Desire — ruling 8

If an adventurer card ends up in exile for any other reason than by exiling itself while resolving, it won't give you permission to cast it as a permanent spell.

Lovestruck Beast // Heart's Desire : règles, fonctionnement et interactions (MTG)

Lovestruck Beast // Heart's Desire is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

This creature can't attack unless you control a 1/1 creature. Create a 1/1 white Human creature token. (Then exile this card. You may cast the creature later from exile.)

How it works : Lovestruck Beast // Heart's Desire

Original English text — Wizards of the Coast / Scryfall

#1October 4, 2019· Wizards of the Coast
You don't have to attack with a 1/1 creature for Lovestruck Beast to be able to attack. You just need to control a 1/1 creature.
No other card is named in this ruling.
#2October 4, 2019· Wizards of the Coast
Once Lovestruck Beast is attacking, it'll remain attacking even if you no longer control a 1/1 creature.
No other card is named in this ruling.
#3October 4, 2019· Wizards of the Coast
If Lovestruck Beast's power and toughness are reduced to 1/1, it learns that loving oneself is the first step on the true path to happiness, and it can attack even if you control no other 1/1 creatures.
No other card is named in this ruling.
#4October 4, 2019· Wizards of the Coast
An adventurer card is a permanent card in every zone except the stack, as well as while on the stack if not cast as an Adventure. Ignore its alternative characteristics in those cases. For example, while it's in your graveyard, Giant Killer is a white creature card whose mana value is 1. It can't be the target of the triggered ability of Mystic Sanctuary.
No other card is named in this ruling.
#5October 4, 2019· Wizards of the Coast
When casting a spell as an Adventure, use the alternative characteristics and ignore all of the card's normal characteristics. The spell's color, mana cost, mana value, and so on are determined by only those alternative characteristics. If the spell leaves the stack, it immediately resumes using its normal characteristics.
No other card is named in this ruling.
#6October 4, 2019· Wizards of the Coast
If you cast an adventurer card as an Adventure, use only its alternative characteristics to determine whether it's legal to cast that spell. For example, if Giant Killer is exiled with the last ability of Vivien, Champion of the Wilds, you can't cast it as Chop Down.
No other card is named in this ruling.
#7October 4, 2019· Wizards of the Coast
If a spell is cast as an Adventure, its controller exiles it instead of putting it into its owner's graveyard as it resolves. For as long as it remains exiled, that player may cast it as a permanent spell. If an Adventure spell leaves the stack in any way other than resolving (most likely by being countered or by failing to resolve because its targets have all become illegal), that card won't be exiled and the spell's controller won't be able to cast it as a permanent later.
No other card is named in this ruling.
#8October 4, 2019· Wizards of the Coast
If an adventurer card ends up in exile for any other reason than by exiling itself while resolving, it won't give you permission to cast it as a permanent spell.
No other card is named in this ruling.
#9October 4, 2019· Wizards of the Coast
You must still follow any timing restrictions and permissions for the permanent spell you cast from exile. Normally, you'll be able to cast it only during your main phase while the stack is empty.
No other card is named in this ruling.
#10October 4, 2019· Wizards of the Coast
If an effect copies an Adventure spell, that copy is exiled as it resolves. It ceases to exist as a state-based action; it's not possible to cast the copy as a permanent.
No other card is named in this ruling.
#11October 4, 2019· Wizards of the Coast
If an object becomes a copy of an object that has an Adventure, the copy also has an Adventure. If it changes zones, it will either cease to exist (if it's a token) or cease to be a copy (if it's a nontoken permanent), and so you won't be able to cast it as an Adventure.
No other card is named in this ruling.
#12October 4, 2019· Wizards of the Coast
If an effect instructs you to choose a card name, you may choose the alternative Adventure name. Consider only the alternative characteristics to determine whether that is an appropriate name to choose.
No other card is named in this ruling.
#13October 4, 2019· Wizards of the Coast
Casting a card as an Adventure isn't casting it for an alternative cost. Effects that allow you to cast a spell for an alternative cost or without paying its mana cost may allow you to apply those to the Adventure.
No other card is named in this ruling.