The fumes are only a 20 foot cone, so Sir Walter will have to be at 75N90E15Z, but then can zip back up. Sir Walter can breathe again in round 377. T-Croc ignores the fumes (rolled 16 Will save).
Round 375: The croc waits.
Buddy charges and the bear closes in. Buddy takes a tentacle AoO for 7. Buddy is at 28 HP. Buddy crits (16+2=18) for 33-10=23 + 6 acid. T-Croc has 35 HP remaining. Buddy is at 80N90E, and the bear is at 70N90E.
Round 376: T-Croc misses with tentacles, but bites Buddy for 3, taking spikes and acidic blood damage in the process. Buddy is at 25 HP, and T-Croc is at 31 HP.
Buddy bites for 13-10=3+4=7. The bear claws twice for 1 and 4. T-Croc is at 26 HP.
Round 377: T-Croc backs up to 80N105E. Buddy and the bear step forward 5 feet.
Buddy bites for 5 total. The bear hits three times for 3. T-Croc is at 18 HP. T-Croc ignores the happy gas. Sir Walter can breathe in round 380.
Round 378: T-Croc backs up to 80N110E.
Buddy bites for 7 total. The bear moves up slowly and can only swing with one paw, hitting for 5. T-Croc has 6 HP remaining.
Round 379: T-Croc hits the bear with two tentacles, inflicting 20 points of damage. The bear has 19 HP remaining.
Buddy misses, but the bear hits for 5. T-Croc has 1 HP remaining.
Round 380: T-Croc hits the bear all three times for 20. The bear disappears.
Buddy bites T-Croc for 7. T-Croc is dying. Buddy is at 80N100E and has 25 HP remaining. Sir Walter is at 60N60E40Z and can breathe.
Round 381: A large, pale green slug oozes into the arena to 80N110E and slams part of its body against Buddy, hitting (rolled 30) for 9, but taking 11 from Buddy's spikes. The slug appears unaffected by Buddy's acidic blood. Buddy has 16 HP, and the slug has 54 HP.