Mascoll was born in Catford, London and started his career with local side Dulwich Hamlet, graduating from the club's Aspire Academy.[4] He made his first team debut for the club on 7 October 2014, when he was substituted on in the 1–0 win over Thamesmead Town in the London Senior Cup.[5] He went on to make another two cup appearances during the 2014–15 season.[5] He made eight appearances for Dulwich at the start of the 2015–16 season before he joined Isthmian League Division One North side Phoenix Sports on loan in December 2015.[6] He went on to be a key player for the club, making a total of seven starts during the loan spell.[6] On 6 February 2016 he joined Isthmian League Division One North side Cray Wanderers on loan instead of returning to Champion Hill.[4] At the start of the 2016–17 season in August, signed for fellow Isthmian League Premier Division rivals Grays Athletic on loan.[7] He went on to make thirty appearances in all competitions for Grays before returning to Dulwich in February 2017, where he played in a number of games in the climax of the season.[8][5]
On 21 August 2017 he signed for EFL League One side Charlton Athletic on a one-year contract following a successful trial and was placed into the under-23 squad.[9] He had previously had a trial at Charlton as an under-16 player but was unsuccessful.[9] He made his professional debut on 1 November 2017 in the 3–2 win over Fulham U23 in the EFL Trophy.[10] He scored his first professional goal in an EFL Trophy tie against AFC Wimbledon on 4 September 2018.[11] On 21 February 2019, Mascoll re-joined Dulwich Hamlet on an initial one-month loan.[12]
Mascoll signed for Wycombe Wanderers on 23 July 2019.[13] After making eight senior appearances that season, he was released.[14]
On 24 August 2020, he joined Bolton Wanderers on a one-year deal.[15] His debut came on 19 September when he came off the bench in the 81st minute, replacing Nathan Delfouneso in a 2–0 defeat to Colchester United.[16] His first goal came on 17 November as he scored Bolton's third goal in a 3–2 win against Newcastle United U21in the EFL Trophy.[17]
On 24 February 2021, he joined League of Ireland Premier Division side Waterford on loan, becoming one of Everton legend Kevin Sheedy's first signings as manager of the club.[18] He made his debut for the club in the opening game of the season on 19 March 2021 as his side lost 1–0 away to newly promoted side Drogheda United.[19] On 19 May 2021, Bolton announced he would be released at the end of his contract.[20] On 25 May 2021, he scored his first goal for Waterford, opening the scoring against Finn Harps at the RSC.[21]
On 9 November 2021, Mascoll signed for National League side Wealdstone.[22] He made his debut four days later, in a 1–0 victory over rivals Barnet.[23] Mascoll scored his first Wealdstone goal on 29 January 2022, finding the net from 30 yards in a 2–1 defeat to Grimsby Town.[24]
On 17 May 2022, Mascoll was one of six players released by Wealdstone following the end of the 2021–22 season.[25]
On 7 October 2022, Lewes announced that they had signed Mascoll.[26]
