Steps to reproduce:
Cast Ulamog, the Ceaseless Hunger, put the "exile 2" cast trigger on the stack
In response, cast Tishana's Tidebinder, and target the Ulamog cast trigger with Tidebinder's ETB
Ulamog's cast trigger is countered, then the Ulamog spell resolves
Ulamog enters with no abilities...
When the opponent has a Dryad of the Ilysian Grove in play, and then you play a Magus of the Moon, their lands keep their basic types.
Timestamps say that since Magus came into play 2nd, it takes priority and the non-basics should lose all basic land types.
Further info:
Modern League, Match...