Board Thread:General Discussion/@comment-84.105.86.39-20190412172020/@comment-2601:283:4600:1EC9:19E4:5514:317A:FDCD-20190420204940

If BTD5, Ice Shards are the best method.

If BTD6, Ice Shards has a pop cap of 30 (?), limiting the number of shards that result, and is thus not good enough for round 63. Recursive Cluster, a bomb tower upgrade (2-0-4), has enough explosions to do very well against 63. 4-0-2 boomerang also works well.