The Summoner's Stage

The Summoner's Stage is the final stage in Collector's Flying Saucer. The only enemy is The Summoner, a boss immune to physical damage with a large health increase compared to previous bosses fought. Even if the previous stages were flown through, many Rogers' and powers may have to be upgraded to beat this difficult level with common consensus among free-to-play players reporting this taking several days of casual play.

Strategy
The Summoner is immune to physical damage. Replace all warrior type weapons with gunslinger and engineer types. Focus on either a team that primarily centers on either paralyzing, resurrection, or lastly raw and pure damage if a capable team is available. Diversification does not provide an advantage here, but including an offensive Roger in the former two recommendations is greatly suggested nevertheless. Ensure offensive Rogers' have the highest health here.

Immediately use a mutagen at the beginning of the fight to reset the power delay and immediately use a healing power afterwards. Nano shields should not be used as tanks are not recommended in this fight.

Don't give up after one attempt. Although unlikely, the frequent changes in RNG may result in enough luck to pass the stage without needing to spend hours upgrading Rogers' or a change in strategy.

If The Summoner was not beaten after many attempts using varying strategies then leveling of Rogers' and acquiring stronger weapons is required. This stage can easily be won when a fifth Roger space is unlocked.