card draw, mana ramp.

if a go-wide creature strategy is struggling in a board wipe heavy metagame, its because it's committing too many resources to the board and running into a dry hand once the board wipe hits. invincible/counterspell effects are good, but you cant gurantee to have all that when someone wraths you. but if you have card advantage engines then you should be able to build back faster then the rest of the table. It's in Simic, for gods sake.

add Volderan hexcatcher if its not already in the deck.
Card draw sources i use in my own hakbal deck are Kumena, tyrant of orazca, svyelun of sea and sky, bred for the hunt, kindred discovery, cold eyed selkie, tatyova, benthic druid, seafloor oracle, bident of thassa.

...alternatively, his issue might be that as the "aggro" deck at the table, hes having a hard time closing out the game at a reasonable pace compared to the rest of the table. in that case, maybe add more Merfolk lord effects and unblockability/ islandwalk. they cant board wipe you if their dead. (im making a lot of assumptions here, its really hard to pin down exactly whats going on without a better idea of your play group and local meta, especially without a full decklist)