Maui stands out as a powerful and versatile card, combining high stats, utility, and resilience for a game-changing impact
Gruul does have some problems with most of the great Gruul cards costing four, but the bigger issue is definitely that green and red just generally get up to pretty different things in Cube
(The copy becomes a token.) A resolving copy of a permanent spell becomes a token, so the token isn't "created." Effects that care about a token being created won't interact with a token that enters the battlefield from Archmage of Echoes's ability
Six toughness makes Phabine less squishy, but Id toss in other protection to reduce your chances of paying commander tax
Karumonix gives your whole army toxic 1, letting you win games quickly by stacking up poison counters
Other than that, however, Flickering is primarily used proactively to reuse enters-the-battlefield triggers