Conclave Sledge-Captain has backup, which says simply "the following abilities". How will this interact with Mutate? (The mutating spell might need flash.)
This is answered by Mark Rosewater in the March of the Machine Learning, Part 2 article:
Backup was created (by Ari Nieh) as another means to show the inhabitants of the various planes working together. The final version kept the essence of the mechanic but had several mechanical hoops to jump through. First up, the original version of the mechanic granted any abilities on the creature to any other creature it targeted with backup. This meant that by granting abilities or through cloning, you could spread abilities that weren't naturally on the backup creatures. To fix this, the mechanic was changed such that it only granted text specifically called out by the card.
This card is now on gatherer, with the following ruling:
Backup confers only abilities that are actually printed below it. Any abilities that are gained by the permanent are ignored, including abilities gained due to a resolving spell or ability or copy effects.