2. Tony Stark (Iron Man 3)
Digitally de-aging actors has become an increasingly common practice over the last couple of years, but no matter how well it's done, you can always tell that it's there, whether it's good (Samuel L. Jackson in Captain Marvel) or bad (Johnny Depp in Pirates 5).
But, in some cases, re-creating or enhancing actors with the use of CGI is done absolutely flawlessly, as was the case with Robert Downey Jr. at the end of Iron Man 3.
Midway through production, the actor suffered an ankle injury which took him out of action for several weeks. Since he was the star of the film and all, there weren't many Downey-less scenes that the filmmakers could shoot while they waited, and with the movie's release date locked in, they had to keep moving in order to get the whole thing finished. So, a solution was devised.
That solution was to digitally re-create the actor for the entire final scene of the film. The closing sequence - in which Tony Stark visits the ruins of his Malibu home and chucks his arc reactor into the ocean - was shot using a body double, with the effects guys adding in RDJ's face during post-production.
The overall effect is truly superb, and some of the MCU's very best CGI, and it really is impossible to spot unless you know it's there.