ANSWERS. . . not really.
If you didn't specify which ones you were answering, I assume that you use that answer for all situations. People with similar responses, except for bonus, are grouped together.
Situation 1.
You grab your opponent (midweight) at 0% and perform a U-throw:
Find the best answer to your opponent doing...
a) No-input (bad DI/stuck in short hitstun)
- B-air (Tenki) - roughly ~25% damage. Some startup lag that can be airdodged or counterattacked by some characters, little ending and landing lag, leaving you free for a followup.
- U-smash (djbrowny, Shadowlink84) - roughly ~20-25% (can be charged, but the initial hits miss). Some startup lag that can be airdodged, but can usually catch airdodges. Pops people upward. Ending lag can be dangerous if DI is predicted incorrectly.
- U-tilt (CaliburChamp, Shadowlink84) - roughly ~17-19% (initial hits miss if you're going for true combo). Fast startup and decent vertical range/priority. There is some commitment time to this attack, so you are still a little vulnerable if DI is predicted wrong.
- Re-grab on landing (Umby) - 12% from U-throw, but it leaves you in control. Much freedom here.
- U-air (ROOOOY!) - roughly ~18-21%. Fast startup, little ending/landing lag, and pops opponent upwards, leaving you free for a followup.
- cheat (darkNES386) - agreeing is not a move. ;p
b) DI towards Sonic's back (correct DI for U-throw- may escape hitstun).
- Pivot U-tilt (djbrowny, CaliburChamp ..kinda, ROOOOY! ..kinda, Shadowlink84) - roughly ~ 17%-19% since the first hit tends to miss or knock people out. However, most characters will be sent out of range of the U-tilt. Can be avoided if your opponent double jumps while free from hitstun.
- Re-grab on landing (Umby, Tenki) - 12% from U-throw, leaves you in control of the match. Countered by double jumping.
- F-air/B-air (Shadowlink84) - roughly ~20-25%, assuming you run after your opponent first. It can be airdodged, and some characters can hit you out of it. This can miss at times if your opponent can double jump.
- U-smash (Shadowlink84) - roughly ~18-22%. Even though U-smash has invincibility frames at some point, assuming that you do this asap out of a run, some characters, like Marth, can hit you in startup lag as you're sliding while starting the smash. Because of startup lag, your opponent can double jump and avoid it.
- cheat (darkNES386)
c) Airdodge
- Re-grab on landing (Tenki, Umby, djbrowny) - 12% from U-throw. Same as usual.
- U-tilt (CaliburChamp) - roughly 12-15% (either complete miss or last hit hits). Pops opponent upwards, but leaves you a little vulnerable.
- SH > Delayed N-air (ROOOOY!, Shadowlink84) - roughly 17-23%. This is a pretty good answer for a correctly-predicted airdodge, regardless of DI. It actually covers all the previous situations pretty well. Little startup and landing lag, but the only problem is its commitment time while in the air, which makes you vulnerable if you miss and your opponent counterattacks.
- U-smash (Shadowlink84) - 16-20% - pops opponent upwards. Again, this is a pretty good way to punish airdodges. Only problematic if you miss.
- cheat (darkNES386)
d) Counterattack (D-air, etc)
- U-smash (djbrowny, ROOOOY!, Shadowlink84) - 16-20%- taking advantage of invincibility frames when possible is good. Getting hit out of it as you're sliding (eg, running U-smash) if your opponent DI's away, or
- Re-grab on landing (Tenki, Umby) - 12% - same as usual. Pshielding counterattacks or running away then grabbing landing lag is not a bad way to start the match.
- U-tilt (CaliburChamp, Shadowlink84) - 15-19%. If the opponent doesn't DI, then U-tilt can combo from a U-throw and outrange some characters' aerials.
- U-air (Shadowlink84) - 15-21%. Thank goodness Sonic's U-air has decent priority. Can be problematic only if your opponent is too low for you to tip with the U-air, or if their DI sends them too far sideways for you to catch with U-air's first hit.
- cheat (darkNES386)
Bonus 1:
Find an answer that answers as many of the above situations as possible at once, and explain how it does so.
- SH B-air FF> Re-grab on landing (Tenki) - [12-25%] B-air takes care of situation A while going for most damage, and shieldgrab camping landing spots takes care of B-D. The only problem here is if the opponent has hitstun resist (Samus.) and hits you before B-air can come out. Or if you miss the grab and/or opponent double jumps.
- Double-take> Re-grab on landing (Umby) - [12%] This is probably the safest option. Keeps you out of range of counterattacks, can help keep you unpredictable, make the opponent feel stupid for airdodging, etc. Just don't miss the landing and you'll be fine.
- SH U-air, follow thier DI into an AAA when you land (djbrowny) - [13-21%] Like the SH B-air option, this hits your opponent if he doesn't airdodge, but has fast enough startup to combo out of U-air on more characters than B-air does. It's nice because U-air has some sideways reach to catch some characters doing backwards DI. Holding A at your opponent's landing spot can hit them out of dodges and/or landing lag. This is escapable, however, by characters with hitstun resist (like Samus), and double jump, if you can't catch the U-air with the first hit.
- SH> (delay)>N-air/(airdodge?) (ROOOOY!) - [12-23%] It's a pretty campy and defensive option, and you'll need pretty good reaction speed if you wanna be able to pull this off well. U-throw>(instant) N-air combos on most characters if they don't airdodge, but it's easier to miss if they DI incorrectly due to its range. If you delay before, N-air, you give your opponent some time to counterattack or double jump, and SH in general can keep you from chasing your opponent's DI since Sonic accelerates slowly in midair. On the up-side, if you miss the N-air and FF out of range of your opponent, it has little landing lag so you can recuperate from the miss.
- U-smash/utilt, depending on DI, but with more priority on U-smash (Shadowlink84) - [12-23%] It makes heavy use of reading the opponent and knowing their trajectories with DI. U-tilt is easily countered avoided by DI towards Sonic's back, and if you miss, you can't really follow it up. U-smash, despite its benefits with priority, some invincibility frames, and airdodge punishment, is avoidable by your opponent double jumping, due to its startup lag. A missed U-smash is also hard to followup from. =[
- Feint via foxtrot/SH> Re-grab [12%] - Well, dNES cheats, so he pretty much does the same as Umby =P. But anyway, foxtrotting gives you the option of punishing an airdodge with an F-smash as well as a grab, and shields a little slower (side-B cancel) if your opponent decides to counter attack and you happen to be foxtrotting inside his attack range. Just avoid those situations and you'll be okay.(darkNES386)
Bonus 2:
Find the best answer to your opponent double jumping out of the U-throw (assuming that your opponent had enough hitstun resist or you didn't attack ASAP). For better answers, take into account that your opponent can double-jump left, up, or right, and at this point, can even attack you.
- SH U-air FF> Re-grab on landing (Tenki) - [12-19%] U-air can either outprioritize or force an airdodge from the opponent, who's rising from the double jump, but it's fast-falled, so it's not really meant to hit anyway. The real meat/point of this move is grabbing the landing. It still sucks to miss grabs though ;_;
- Double-take> Re-grab on landing (Umby) - [12%] Safe, keeps you in control. Don't miss grabs.
- Full hop U-air. (djbrowny) - [17-19%] Can outprioritize most aerials from opponents. However, since your opponent has more time/space, it's airdodgeable. Just don't do a rising U-air while your opponent is falling and airdodging through you or the roles will be reversed.
- Shieldgrab camp on high priority aerial chars, aerial on more vulnerable chars (ROOOOY!) - [12%-25%] Shieldgrab camping is pretty safe for the most part, as stressed enough with Umby's singular answer-to-all post. Making your followup based on what character you're fighting is important. Not bad `.`; Again, don't do rising aerials while your opponent is falling towards you. It screws up spacing if you're trying to U-air tip, or sets you up for an opponent's attack if he airdodges through you.
- Chase > Character-specific reactions: bait/punish counter attack, U-air aggressively, camp the landing (Shadowlink84) [12%+] Too general. Answers everything XD. Really though, character-specific reactions are good.
- Feint via foxtrot/SH> Re-grab (darkNES386) - Same as before. Don't miss grabs `.`;
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If you have any issues on these comments, feel free to point out and correct them. I started to get lazy for the bonus ones, even though they were the most important and are important for the main point of the question. lol.