Is Escape an Activated Ability
No, there is no difference between blink and flicker in MTG

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You dont need combos to win with lifegain the incremental drain plan closes games on its own but knowing they exist shapes your deckbuilding and your threat assessment at the table
The actual number of clerics, wizards, rogues, and warriors is irrelevant
Captain is fine but likely a powerful stand alone card without synergy would be as good if not better, I just like to go deep on things when trying them out