Marubozus are an interesting candle pattern wherein the close and open of the candle are also the high / low points of the candle. In other words, a candle with no shadows or wicks.
How reliable are they, though? Probably not very reliable on their own. It may also depend on the size of the candle. You would probably want to incorporate this candle pattern with other filters, like RSI, MACD, to filter trade opportunities.