NOTE: THIS IS MAINLY ON THE CONSOLE PORTS OF SFIII, SPECIFICALLY THE ONLINE EDITION ON PS3.
NEUTRAL
Gill's neutral will mainly consist of his cr.MK, 5LK, and 5MK. The first 2 are safe on block and may give way to potential knockdowns. Some of Gill's normals, like 5LP, can be linked into his other normals, (5LP>5MP,2LK>2MK, etc...) for decent damage, but no real combo potential. Your main goal is to back the opponent into a corner for more pressure or stun them. Gill thrives on a cornered opponent, especially when he's on the P1 side. This can be done with a combo from midscreen that ends in 5HP on P1 side, and Lariat loops on P2 side. From there, a hard knockdown is ideal, as to set up okizeme for Gill, and potentially start a new combo or extend pressure. A stun is especially ideal, as this guarantees a TOD or Seraphic Wings hitting, in both cases, big damage.
OFFENSE
cr.HP > Lariat > Lariat > Lariat (stun) > cr.HP > Lariat > Lariat > Lariat. This is the combo Gill needs to pull off, the near universal TOD. When on offence, one single 2HP, or j.HP/HK can seal the opponent's fate. There are several TOD routes Gill can take, some character exclusive, others able to be done on the entire cast. Going for combos that stun or give a knockdown, can also help continue the pressure. Air resets into Meteor strike almost guarantee big damage for Gill and a knockdown, but parrying is an option despite how hard it might be for the opponent. Momentum is Gills glue, what holds his character together. In the right hands, Gill can be an offensive powerhouse that can kill the entire cast in less than 20 seconds and overwhelm any defensive master into opening up.
DEFENSE
Gill is ideally not playing defense. But he's got plenty of tools that can get him out. For jump-ins, 2HP, 5HK, 4MP, and even 236M/HP are all good anti-airs that can lead to small juggles, he can also go for j.HP/K for better combo potential. When dealing with pressure in the corner, Gill can parry and go for a TOD with 2HP or use a safer button like 2MK to potentially get out of the corner. You won't really be in these situations too often if you're playing Gill, though.
SUPER ARTS
Meteor Strike is your best one but is really situational, sometimes usable in TODs against characters with bigger stun and health bars, Air resets into this also deal good damage if pulled off. Seraphic Wings oddly isn't that bad. It can be the ender for certain TODs, but really, it's just used to be flashy. Decent as okizeme as it does a lot of chip damage and is unparryable as far as testing has us know, despite videos of people supposedly parrying the other 19 hits of Seraphic Wings (The first hit is entirely unparryable, the other 19 aren't really known). Resurrection, despite how useful it might sound, is awful. Breaks your super meter for the rest of the round. It's extremely punishable as well.
THINGS TO AVOID
If it is possible, AVOID RESURRECTION. Resurrection is extremely easy to punish with any normal, leaving him at close to 0 health. You lose out on the potential punishes and damage with Meteor Strike and Seraphic Wings for the round, and while not essential for Gill's gameplan, is still a loss Gill would rather not take. Moonsault Kneedrop is Gills worst move, and surprisingly, can be a contender for worst move in the game. It is extremely inconsistent with its frame data, as in some cases, Gill is slightly more minus or plus on some characters. Gill is only plus on a crouching character (except for Hugo). The only real damage he can get after it is a 2MK if he manages to hit a crouching opponent with it. Taunting is also pretty useless. It has its place in a small handful of scenarios, but it's hard to pull off, and if he gets hit, no benefit comes of it. Do not do Gills taunt. It's basically useless.
SUMMARY
That's really it. Gill is an extremely easy character with surprisingly easy combos, and a rather straight forward gameplan for such a cheap character. And despite what he claims himself, no he is not perfect. Just really good. Good luck playing in any tournament that might use a console port though. Cause they probably don't exist. And if they do, they probably banned Gill Anyway.