relics/RelicTriangleRuler.cs
using Sandbox;
using System.Reflection.PortableExecutable;
using System.Runtime.Versioning;
using System.Threading.Tasks;

public class RelicTriangleRuler : Relic
{
	public override bool ShouldHandleEvent( EventType eventType )
	{
		return eventType == EventType.Match && Manager.Instance.Stats[StatType.NumMatches] % (5 - Level) == 0;
	}

	public override async Task HandleEventAsync( EventType eventType )
	{
		List<Card> validCards = new();

		CheckCornerCard( new IntVector2( 0, 0 ), validCards );
		CheckCornerCard( new IntVector2( 0, Manager.Instance.GridHeight - 1 ), validCards );
		CheckCornerCard( new IntVector2( Manager.Instance.GridWidth - 1, 0 ), validCards );
		CheckCornerCard( new IntVector2( Manager.Instance.GridWidth - 1, Manager.Instance.GridHeight - 1 ), validCards );

		if ( validCards.Count == 0 )
			return;

		validCards.Shuffle();

		var cardToReveal = validCards.First();

		await Task.DelayRealtime( 300 );

		Manager.Instance.PushEventMessage( this, eventType );

		await Task.DelayRealtime( 100 );

		Manager.Instance.PlaySfxCenter( "triangle_ruler", volume: 0.3f, pitch: Game.Random.Float( 1.5f, 1.55f ) );

		await Task.DelayRealtime( 200 );

		Manager.Instance.PlayCardSfx( "card_flip", cardToReveal, volume: 0.8f, pitch: Game.Random.Float( 1.15f, 1.2f ) );
		await Manager.Instance.RevealCard( cardToReveal );

		await Task.DelayRealtime( 850 );

		Manager.Instance.PlayCardSfx( "card_flip", cardToReveal, volume: 0.7f, pitch: Game.Random.Float( 0.65f, 0.75f ) );
		Manager.Instance.HideCard( cardToReveal );

		await Task.DelayRealtime( 350 );

		Manager.Instance.PopEventMessage();
	}

	void CheckCornerCard( IntVector2 gridPos, List<Card> cards )
	{
		var card = Manager.Instance.GetCardAtGridPos( gridPos );

		if ( card != null && !Manager.Instance.ChosenCards.Contains( card ) && !card.IsRevealed )
			cards.Add( card );
	}
}