Those odds sound generous to me. Put me down for 20 on Guthok.
Round 446: Guthok misses with claws, but kills the spider with his bite, then swings around and bites the ant (rolled 24) for 18 points of damage. The ant has 9 HP remaining.
The ant hits with all three attacks, for a total of 20. Guthok has 83 HP remaining, but resists the poison.
Round 447: Guthok only hits with one claw, inflicting 7. The ant is at 2 HP.
The ant hits with claw and sting for 12. Guthok is at 71 HP and resists the poison.
Round 448: Guthok misses all three times (best roll 23).
The ant hits with claw and sting for 17. Guthok is at 54 HP and resists the poison.
Round 449: Guthok hits with bite for 8 and finally fells the ant, who is dying. Guthok has 54 HP remaining, and is at 60N40E.
First in round 450: A 12 foot tall mushroom with clubbed hands enters the arena to 60N15E, and shoots a line of spores at Guthok, which hit (rolled 17 ranged touch). Guthok feels peaceful (rolled 12 Will save). Until notified, Guthok can only take a partial action each round, and not attack at all. So, Guthok, what's next?