Goku (Super/GT)

Goku from What #5 is one of the many Goku's in the [What If] Series. This incarnation of Goku is from a timeline where GT happened after Super, thus allowing him to combine Super Saiyan 4 and Super Saiyan Blue.

Appearance
He takes the appearence of GT Goku. As a SSGSS4, he looks like the standard Super Saiyan 4 with the exception that his fur and hair color is blue.

Personality
Managed to combine Super Saiyan 2, 3, and 4 with Godly Ki and so is likely smarter than his canon counterparts.

Power
In the [What-If Universe Official Power Scaling ], Goku is ranked as follows:


 * Rank 19 (Super Saiyan Blue)
 * Rank 7 (Super Saiyan Blue + Super Saiyan 4)

In his SSGSS4 form, Goku's power can best be described as absolutely monstrous, with Golden Cell himself calling Goku "a monster" after sensing the sheer power of this form.

Keep in mind that Golden Cell in What-if 5 is ranked 2 spots above where normal SSJ Blue Goku was in the same what-if (implying at least a decent power gap between Golden Cell and normal SSJ Blue), and is one spot above SSJ God Gogeta from What-if 12, meaning this Golden Cell matched if not exceeded the SSJ God Fusion in strength.

Also, this incarnation of Goku is one spot above Full-Power Beerus from what-if 8 in the official power-ranking video, meaning that he is at least as strong as Beerus but could likely be somewhat stronger. He is also said to be the strongest incarnation of Goku to ever exist, but it is unknown if it is referring to canon Goku or just the versions of Goku on the power-scaling chart, with the latter assumption being far likelier but also far less impressive in terms of context (since the former would include Ultra Instinct [which is unlikely but not impossible since both UI Goku and SSGSS4 surpass Beerus], while the latter would only go up to SSJB + Kaioken-10x Goku, whom this Goku already surpasses in normal SSJB alone).

Also, if you were to accept the statement in one of the DBGT handbooks that SSJ4 Goku is on par with SSJ1 Vegito (although SSJ4 may have exceeded this given that this handbook was meant for Baby-arc Goku, who grew greatly in power during the later Dark Dragon Balls-Arc), then by doing some power scaling equations with multipliers, you would find that a SSJ4 Blue Goku is at least comparable in power to a fusion with the "normal" SSJ Blue form. Keep in mind that Gogeta in normal SSJB absolutely wrecked a FPSSJ Broly in the canon DBS Broly movie, and Broly in that state is "probably" stronger than Beerus. Even ignoring that Goku's much higher base power level in this what-if and Goku in DBGT surpassing the power that matched SSJ Vegito both heavily imply that SSJ4 Blue Goku is probably above SSJ Blue Gogeta from the movie, this power-scaling would support the claim that SSGSS4 Goku surpasses Beerus in power.

Aside from his immense power, the SSJ4 part of his transformation likely retains the original form's advantage of minimal power/stamina drain, meaning that Goku can probably maintain this form for long periods of time.

Even in his "normal" SSJ Blue form, however, Goku still has a ridiculous amount of power as a result of 30 years to train his abilities. Even with the power decrease from being turned into a child by Pilaf's wish, Goku's SSJB form still surpasses all his other what-if incarnations' best forms, even their SSJB + Kaioken-10x forms. He also surpasses Golden Cell (from a different what-if) after the latter had gotten God Ki (keep in mind that even before this absurd power up, Golden Cell from that what-if had stomped SSJB Goku and Vegeta along with SSJB + Kaioken-10x Goku), and is just below SSJ God Gogeta from what-if 12, since he is only one rank below the SSJ God Fusion in the official power scaling video. Considering that base Gogeta is at least as strong as SSJB Goku or Vegeta individually (going by the DBS Broly movie), this speaks volumes about Goku's insane power after 30 years.