Short answers, pulled from the story.
The Second Italo-Ethiopian War began on the 3rd of October 1935, when Italian forces crossed the Mareb River into Ethiopia without a declaration of war, and ended with the fall of Addis Ababa on the 5th of May 1936. Conventional military operations concluded that month, though Ethiopian resistance to Italian occupation continued until the country was liberated in 1941.
Yes. Italian forces used between 300 and 500 tons of mustard gas against both military and civilian targets, violating the 1925 Geneva Protocol. Mussolini authorized the use of gas on the 27th of October 1935, weeks before the campaign began, and expanded the authorization on the 28th of December 1935 to include use "on a vast scale." Red Cross units and hospitals were among the targets attacked.
The League of Nations imposed economic sanctions on Italy in November 1935, approved by 50 member states, but they excluded oil, coal, and steel, the materials most critical to Italy's war effort. Britain did not block Italian ships from using the Suez Canal. The United States, not a League member, continued supplying Italy with essential goods, and Britain and France both preferred Italy as an ally against Germany over taking strong action.
Haile Selassie personally commanded the final Ethiopian offensive at the Battle of Maychew on the 31st of March 1936. After the defeat, he was forced into exile, boarding a train in Addis Ababa on the 2nd of May 1936 with the gold of the Ethiopian Central Bank and fleeing to the United Kingdom. He was restored as emperor on the 5th of May 1941, exactly five years after the fall of the capital, when Allied forces liberated Ethiopia.
On the 19th of February 1937, Eritrean rebels Abraham Deboch and Mogos Asgedom attempted to assassinate the Italian Viceroy Marshal Rodolfo Graziani. Italian forces responded with three days of mass killing ordered by Federal Secretary Guido Cortese. A 2017 historical study estimated 19,200 people were killed, representing 20 percent of Addis Ababa's population. The date is commemorated in Ethiopia as Yekatit 12.
Italy sent approximately 685,000 soldiers to East Africa, supported by 6,000 machine guns, 2,000 pieces of artillery, 599 tanks, and 390 aircraft. Ethiopia mobilized between 350,000 and 760,000 men, equipped mainly with repeating rifles; the Ethiopian Air Force had 13 aircraft and four pilots at the outbreak of the war. The Italian mobilization is regarded as the largest colonial army ever assembled.