This strategy which has no stop loss and therefore is a high risk strategy, goes long as soon as the "S&P 500" on "OANDA" or "FXCM" starts a downtrend. A Bollinger Band filters the more extreme downtrends. The Bollinger Band setting can be changed to filter selectively for even more severe price declines or to allow more trades by setting the standard deviation to a lower value.
This "S&P 500" strategy only correctly works as intended on "OANDA" or "FXCM" (with default setting "OANDA"), because "OANDA" or "FXCM" are the only two price sources allowed in the strategy.
If you don't want to lose all your money due to some random strategy you found on the Internet, here is a warning: All trading involves high risk; past performance is not necessarily indicative of future results.
P.S. Here are more trade examples, which help to explain why I named this a high risk strategy: